CELLS and DNA

CELLS and DNA

INHERITANCE TOPIC 3 - 2017 INHERITANCE Things to cover Review Genes of Topics 1 & 2 & alleles Heterozygous & homozygous Genotypes & phenotypes Dominant traits & recessive traits Autosomal & sex-linked traits Punnett Squares & pedigrees

REVIEW REVIEW TOPIC 1 cells nucleotides phosphate double

helix covalent nitrate 4 pentose hexose phosphorus linear hydrogen

nitrogen 2 DNA is composed of _______________. Each nucleotide consists of: A _______________ sugar A _______________ group A _______________ base (_____ types) The subunits form chains. Two chains twist to form the _______________ shape of the DNA molecule. Chemical bonds hold the DNA molecule together. Strong _______________ bonds hold the nucleotides together, while weak _______________ bonds form between the bases. REVIEW TOPIC 1

DNA is composed of nucleotides. Each nucleotide consists of: A pentose sugar A phosphate group A nitrogen base (4 types) The subunits form chains. Two chains twist to form the double helix shape of the DNA molecule.

Chemical bonds hold the DNA molecule together. Strong covalent bonds hold the nucleotides together, while weak hydrogen bonds form between the bases. REVIEW TOPIC 2 autosomes 2 pairs chromosomes centrosomes thymine

sex chromosomes cytosine 23 pairs DNA is coiled up tightly to form _______________ There are _______________ of chromosomes in every cell. o Most of these are _______________ , controlling general characteristics. o One pair are the _______________ , controlling both sexual and general characteristics. REVIEW TOPIC 2 autosomes

2 pairs chromosomes centrosomes thymine sex chromosomes cytosine 23 pairs DNA is coiled up tightly to form chromosomes There are 23 pairs of chromosomes in every cell.

o Most of these are autosomes, controlling general characteristics. o One pair are the sex chromosomes, controlling both sexual and general characteristics. REVIEW TOPIC 2 growth mitosis gamete s asexua l

identic al 46 23 differentiation meiosi s sexual larger

repair smaller 4 2 non-identical Cell division is necessary for _______________ , _______________ and reproduction.

One type of cell division, _______________ , is used in the formation of new body cells. It is also used by unicellular organisms for _______________ reproduction. The ______ daughter cells formed are _______________ to the parent cell and have ______ chromosomes. The other type of cell division, _______________ is used to form sex cells. Another name for the products of this type of division are _______________. This process takes place in the reproductive organs. The ______ daughter cells formed are _______________ to the parent cell and have ______ chromosomes. They are also _______________ in size. REVIEW TOPIC 2 replicate

mutants trisomy monosomy mutations chromosome s genes an extra differentiate a missing

In order for cell division to occur, the DNA must ____________________ and the chromosomes must divide equally between the cells. ____________________ can occur if this does not happen correctly. For example, disorders involving additional or missing ____________________. Down Syndrome is one example. This disorder results from the presence of ____________________ Chromosome 21. This is called ____________________ 21.

REVIEW TOPIC 2 Cell division is necessary for repair, growth and reproduction. One type of cell division, mitosis, is used in the formation of new body cells. It is also used by unicellular organisms for asexual reproduction. The 2 daughter cells formed are identical to the parent cell and have 46 chromosomes. The other type of cell division, meiosis, is used to form sex cells.

Another name for the products of this type of division are gametes. This process takes place in the reproductive organs. The 4 daughter cells formed are non-identical to the parent cell and have 23 chromosomes. They are also smaller in size. REVIEW TOPIC 2 In order for cell division to occur, the DNA must replicate and the chromosomes must divide equally between the cells. Mutations can occur if this does not happen correctly. For example, disorders involving additional or missing chromosomes. Down Syndrome is one example. This disorder results from the

presence of an extra Chromosome 21. This is called Trisomy 21. VARIATION VARIATION The population of the Earth is more than 6 billion people, and no two individuals (apart from identical twins) are genetically the same. Why? People are different because they inherit different characteristics (or traits) from their parents. Children carry a unique set of genes; half from their mother and half from their father.

VARIATION Some characteristics, such as eye colour and earlobe shape, are only determined by genes. These are called inherited characteristics. Other types of characteristics, such as scars and hair length, are not inherited but depend on environmental factors. These are called acquired characteristics. In some cases, it can be difficult to say how much influence the environment has over the expression of a trait. VARIATION All the observable characteristics of an

organism are called its phenotype. The full set of genes of an organism is called its genotype. An organisms phenotype therefore depends on its genotype plus environmental conditions. VARIATION Sexual reproduction is the most important cause of genetic variation because it mixes up genetic material. Meiosis creates a variety of gametes Any male gamete can combine with any female gamete during fertilisation. Mate selection is random.

All these events occur randomly and create new combinations of genetic material. VARIATION Mutation is the change in the genes or sequence of DNA and is therefore another cause of genetic mutation. Mutations can arise randomly; for example: through the incorrect copying of base pairs during DNA replication Uneven distribution of chromosomes during cell division Mutations can also be caused by mutagenic agents, such as radiation and certain chemicals. These factors

are called mutagens. Some mutations may be beneficial, but many are harmful and increase the risk of diseases such as cancer. GENES VS ALLELES GENES The basic unit of inheritance A segment of DNA base sequence Control one specific characteristic. Contain the code needed to produce a protein. Located in the same position on the

same chromosome. This position is called its locus. ALLELES Different versions of a gene Code may only differ by a few bases: eg. The base eye colour gene has 2 options: blue and brown Chromosome Gene AGTACGGTACG = blue eyes allele (b) AGTCAGGTACG = brown eyes allele (B) This diagram shows one chromosome,

with ten genes. There are 20 alleles shown (two for each gene) in various combinations. a A B b c C D

D e E f f G G h

H i i J j EXPRESSION All alleles contain a base sequence (code) that is used by the cell to synthesise (build) a protein. eg. eye colour pigment The allele that will have its code used is determined by

its dominance. DNA protein gene expression DOMINANCE Most genes are controlled by 2 alleles. Some alleles are dominant over others, so some traits can be hidden (= recessive) by others (eg. blue eyes) DOMINANCE Dominant alleles: always expressed in a cells phenotype only one copy of the dominant allele needs to be inherited in order for it to be expressed represented by an upper case letter (eg. B)

Recessive alleles: only expressed in a cells phenotype if two copies are present if only one copy is present, its effect is masked by the dominant allele represented by an lower case letter (eg. b) HOMOZYGOUS If the alleles for a characteristic are the same, the organism is said to be homozygous for that trait. If there are two dominant alleles, the organism is said to be homozygous dominant

for that gene. If there are two recessive alleles, the organism is said to be homozygous recessive for that gene. HETEROZYGOUS If the alleles for a characteristic are different, the organism is said to be heterozygous for that trait. The protein made (and trait expressed) will depend on which allele is dominant and which allele is recessive.

The allele for brown eyes is dominant over the allele for blue eyes. The individual will have brown eyes, because the allele for brown eyes masks the allele for blue eyes. TYPES OF INHERITANCE TYPES OF INHERITANCE 1) Complete dominance 2) Co-dominance COMPLETE DOMINANCE Complete dominance = NORMAL!!!!!

If the dominant allele is present, it will be expressed eg. Brown eyed allele (B) always expressed when present (BB or Bb) Notation used: Choose 1 letter Use lowercase (recessive) and uppercase (dominant) eg. BB, bb or Bb only B trait shown CODOMINANCE There is no dominant allele! The phenotype is a blend of both alleles present eg. red allele + white allele = pink phenotype

eg. Type AB blood from combination of A and B alleles Notation used: Choose 2 letters Use uppercase for both eg. RR, WW or RW mixture of R & W traits is shown AWESOME EXAMPLE: ABO BLOOD GROUPING To determine your blood type, there are three alleles: A IA B - IB and O-

The alleles IA and IB are codominant However, both of these alleles are completely dominant over This results in four different phenotypes. ABO BLOOD GROUPING Phenotype or blood group Type A Type B Type AB Type O Genotypes IAIA or IA IBIB or IB

IAIB TYPES OF INHERITANCE 3) Autosomal inheritance 4) Sex-linked inheritance AUTOSOMAL INHERTIANCE Autosomal inheritance = NORMAL!!!!! The gene is located on an autosome Traits can be: autosomal dominant meaning that a trait/disorder is determined by the presence of a dominant allele autosomal recessive determined by the presence of two recessive alleles

Notation used: BB, bb, Bb SEX-LINKED INHERTIANCE The gene is located on a sex chromosome Can be either the X chromosome or the Y chromosome (but is usually X) eg. haemophilia, colour blindness Traits can be: sex-linked dominant meaning that a trait/disorder is determined by the presence of the dominant allele on the X chromosomes sex-linked recessive meaning that a trait/disorder is determined by the presence of one or two recessive alleles on the X

chromosomes SEX-LINKED INHERTIANCE Notation used: Females: Homozygous XNXN or XnXn Heterozygous XNXn (carrier) Males (only one X chromosome): Unaffected XNY Affected XnY Why are there no male heterozygotes?? CARRIERS

Someone who is heterozygous for a genetic disorder They do not have the disorder themselves However, the disorder can be passed on to the next generation eg. CC = no Cystic Fibrosis cc = Cystic Fibrosis Cc = carrier of CF PUNNETT

SQUARES PUNNETT SQUARES Also called monohybrid crosses Method used to find the expected genotype and phenotype ratios of offspring when the parental genotypes and/or phenotypes are known. PUNNETT SQUARES Steps: 1. Write down the parental genotypes You may need to choose letter to represent your trait choose easy ones like T, G, H not C, S, Y 2. Write down the possible alleles that they are able to 3.

4. 5. 6. pass on in their gametes (sex cells) Construct the Punnett square Fill in the potential genotypes of the offspring Determine the genotype ratio of the offspring Determine the phenotype ratio of the offspring PUNNETT SQUARES Example: An alien that is homozygous dominant for green skin has chosen an alien who has purple skin for his bride. Determine the likelihood that their children will have

purple skin. Like in Maths you need to state what symbols you will be using to represent your traits: eg. Let G = green; g = purple PUNNETT SQUARES Answer: Parents: GG and gg Gametes: G and g First generation (F1): G G

g Gg Gg g Gg Gg F1 genotype ratio: 100% Gg F1 phenotype ratio:

100% green skin PUNNETT SQUARES Example: One of the couples sons (named Neyp) married a female alien (named Gjup) who was homozygous recessive for the skin colour trait. Work out the genotype and phenotype percentage of their potential offspring. PUNNETT SQUARES Answer: Parents: Gg and gg Gametes: G,g and

g Second generation (F2): g G g Gg gg F2 genotype ratio: 50% Gg : 50% gg F2 phenotype ratio: 50% green skin : 50% purple skin

PUNNETT SQUARES Example: One of Neyps sons married a female alien who was heterozygous for haemophilia. Neyp did not have haemophilia. Calculate the likelihood that they could have a child with haemophilia. Again specify your symbols! It is a sex-linked recessive disorder!!! So: Let H = normal; h = haemophilia PUNNETT SQUARES Answer: Parents: XHXh and XHY

Gametes: XH, Xh and XH, Y First generation (F1): XH Xh XH XHXH XHXh Y XHY X hY

F1 genotype ratio: 25% XHXH : 25% XHXh : 25% XHY : 25% XhY F1 phenotype ratio: 75% normal: 25% haemophilia PEDIGREE CHARTS PEDIGREE CHARTS Shows the members of a family and how they are related to each other. A genetic family tree! Pedigree charts can also be used to study the inheritance of a characteristic.

PEDIGREE CHARTS Circles = females Squares = males Shading = affected individuals Parents = linked by a horizontal line Children = vertical lines running down from parents Siblings = linked by a horizontal line above them PEDIGREE CHARTS Example: Draw a pedigree chart for Neyp and his wife Gjup, including their parents and children. They had 3 children, 2 boys and a girl (in order of age): Their youngest son (Guol) had green skin and was

also married with one purple daughter (Zcug). Their daughter (Hefg) had purple skin and married an alien who also had purple skin. They had one son (Yerg). NB. Being purple is the recessive trait! PEDIGREE CHARTS ? ? I gg GG Gg/gg

Gg/gg II III Gg gg ? ? Gg/gg

Gg/gg Gg gg gg IV gg gg PEDIGREE CHARTS Pedigree charts can also be used to determine if: The characteristic is dominant or recessive.

The characteristic is sex-linked or autosomal. Things to look for: Gender bias of males:females more males indicates sex linkage; balanced ratio indicates autosomal Affected offspring from unaffected parents indicates a recessive condition Affected sons from affected fathers indicates an autosomal condition

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