Genetics Quick Review of Grade 11 Sex Linked Traits Sex Influenced Traits Polygenic Traits Epistatic Genes

How many chromosomes do humans have? 46…or 23 homologous pairs 23 from your mother and 23 from your father Pairs1 through 22 = autosomal chromosomes Which chromosomes determine if you’re a girl or boy?

Two Types of Chromosomes Two Types of Cells Somatic Cells – All body cells, diploid (2n) Sex Cells – Gametes, haploid (n) Two Types of Chromosomes Autosomal – All body cells Sex Chromosomes – X and Y

The Sex chromosomes Its all up to Dad…. If you get a X you’re a girl

The Sex chromosomes But... If you get a Y you’re a boy

Punnett Squares X X X XX XX Y XY XY

Phenotype Genotype Allele Homozygous Heterozygous Expressed trait (physical appearance) Phenotype The set of genes that an organism possesses Genotype Allele Different forms of the same gene When two alleles are identical Ex. DD Homozygous When the two alleles are different Ex. Dd Heterozygous

Dominant Allele which controls the characteristic whenever it is present. BB or Bb recessive Allele whose characteristics only show up when it is present on both chromosomes bb

Genetics Quick Review of Grade 11 Sex Linked Traits Sex Influenced Traits Polygenic Traits Epistatic Genes

Sex Linked Traits Sex-linked traits are traits that are controlled by genes on the sex chromosomes Examples: Colour Blindness Hemophilia

3 Different Forms of Sex Linked Inheritance X-linked recessive inheritance X-linked dominant inheritance Y-linked inheritance

Sex Linked Inheritance Notation X-linked recessive alleles are represented by a X with a superscript of either: + (dominant) or – (recessive)

Genotypes of Sex Linked Inheritance What are the possible genotypes of a sex linked inheritance for a female? X+X+ X+X - X -X - What are the possible genotypes for sex linked inheritance for a male? X+Y - X - Y

1. X-linked Recessive Inheritance X-linked recessive traits are traits resulting from a recessive allele on the X chromosome

Why do X-linked recessive traits show up more often in men than women?

Are YOU Colorblind? Normal Color Vision: A: 29, B: 45, C: --, D: 26 Red-Green Color-Blind: A: 70, B: --, C: 5, D: -- 3. Red Color-blind: A: 70, B: --, C: 5, D: 6 4. Green Color-Blind: A: 70, B: --, C: 5, D: 2

X-linked Recessive Inheritance Example #1: Colorblindness The allele that controls colorblindness is found on the X chromosome and is recessive What genotype must a female have to be diagnosed as colorblind? X -X-

Possible Colorblindness Phenotypes X+X+ Female with Normal Vision X+X – Female with Normal Vision (Carrier) X -X – Colour Blind Female X+Y – Male with Normal Vision X – Y Colour Blind Male

Let’s try a cross: X+X– • X+Y Phenotypes Females: Males:

Let’s try a cross: X+X– • X-Y Phenotypes Females: Males:

Let’s try a cross: X+X+ • X-Y Phenotypes Females: Males:

Let’s try a cross: X-X- • X+Y Phenotypes Females: Males:

Try these questions on your own: A woman who is heterozygous (a carrier) for colorblindness marries a man with normal vision. What will be the possible phenotype ratio of their children? What is the probability that the sons of a homozygous recessive mother would be colour blind? *Remember to represent colorblindness with a “-”

More examples of X-linked Recessive Inheritance Example #2: Hemophilia Hemophilia is a serious ailment in which the blood lacks a clotting factor, and therefore when an individual is injured, they cannot stop bleeding About 1 in 4,000 males are born with disorder, much lower incidence in females

Hemophilia Pedigree

Just to make sure you got it! ;) A woman who is heterozygous for hemophilia marries a normal man: a. What are the genotypes of the parents? b. Make a Punnett square for the cross c. What is the probability that a male offspring will have hemophilia? d. What is the probability of having a hemophiliac female offspring?

2. X-linked Dominant Inheritance X-linked dominant traits are traits that result from the presence of a dominant allele on the X chromosome Unlike X-linked recessive traits, females and males both require only ONE dominant allele in order to express the trait

X-linked Dominant Inheritance Example #1: Faulty Tooth Enamel and Dental Discoloration Individuals who have an X chromosome that carries a dominant allele for this trait will have dental discoloration.

Possible Dental Disorder Phenotypes X+X+ Female with Dental Discoloration X+X – X -X – Normal Female X+Y Male with Dental Discoloration X – Y Normal Male

Let’s think about it... Would a heterozygous woman for dental discoloration display the trait? Yes, because dental discoloration is a X-linked dominant trait, so only one dominant allele is needed to express the trait What percentage of the children from a heterozygous mother and an affected father would have dental discoloration?

3. Y-linked Inheritance Y-linked traits are controlled by alleles on the Y chromosome Another word for Y-linked traits is holandric traits (“wholly male”) Are females affected by Y-linked traits? Do the words homozygous or heterozygous apply to Y-linked traits?

What do these 2 have in common? Example of Y-Linked Inheritance – HAIRY EARS! Anthony Victor (India) has hair sprouting from the centre of his outer ears (middle of the pinna) that measures 18.1 cm (7.12 in) at its longest point.

All of the sons of an affected male will display this Y-linked trait

Last Sex-linked Trait Example Eye color in fruit flies (Drosophilia melanogaster ) Eye color is controlled by the X chromosome Red eyes are dominant to white White eyes are most common in males Females only display white eyes if they are homozygous recessive for the trait

Fruit Flies Continued What type of X-linked inheritance is this? Try your new knowledge out on the handout you are about to receive! X-linked recessive Inheritance because the males show the trait more often that the females. Also, the females must have two X chromosomes, both of which carry the recessive alleles for white eye color in order to have white eyes!

Genetics Quick Review of Grade 11 Sex Linked Traits Sex Influenced Traits Polygenic Traits Epistatic Genes