Presentation on theme: "Biology Genetics Part 2 b Objectives: a) Review Mendelian Genetics b b) Types of cells/Types of Chromosomes b c) Sex linked traits b d) Sex Influenced."— Presentation transcript:
Biology Genetics Part 2 b Objectives: a) Review Mendelian Genetics b b) Types of cells/Types of Chromosomes b c) Sex linked traits b d) Sex Influenced traits b e) Polygenics b f) Epistasis
Cells b We have 2 types of cells b 1. Somatic Cells (2n) – body cells b 2. Sex Cells (n) – sperm and egg
Chromosomes b We have 2 types of Chromosomes: b 1. Autosomal chromosomes – pairs 1 through 22 in humans (non-sex chromososmes) b 2. Sex chromosomes – xx or xy b What about a fruit fly with a 2n = 8?
Definition b Sex-linked traits are traits that are controlled by genes on the sex chromosomes The X and Y chromosomesThe X and Y chromosomes
Are they controlled by both sex chromosomes? b Most sex-linked traits are controlled by genes on the X chromosome. b This is because an X chromosome is much larger than a Y chromosome. b A few traits are suspected to be controlled by genes on the Y chromosome, however there is less research about Y-linked traits.
Different Forms of Sex-linked Inheritance b There are three different forms of sex- linked inheritance that we will be examining: X-linked recessive inheritanceX-linked recessive inheritance X-linked dominant inheritanceX-linked dominant inheritance Y-linked inheritanceY-linked inheritance
X-linked Recessive Inheritance b X-linked recessive traits are traits resulting from a recessive allele on the X chromosome. b There are over 100 different human conditions that are caused by recessive alleles found on the X chromosomes. b X-linked recessive alleles are represented by a X, superscript lower case letter or a plus/minus b (+/-)
X-linked Recessive Inheritance b These traits tend to show up in males more than females. Why?Why? Because males only carry one X chromosome! ( they have one x chromosome, and one Y chromosome that make up their sex chromosomes).
X-linked Recessive Inheritance b Example #1: Colorblindness b The allele that controls colorblindness is found on the X chromosome and is recessive. b What genotype must a female have to be diagnosed as colorblind? Homozygous recessive (X - X - )
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
Try this problem! b What is the probability that the sons of a homozygous recessive mother would be colorblind? b Represent colorblindness with a “-” Mothers Genotype X - X - Each son would receive an X chromosome from their mother which means… Each son would have an X chromosome with a recessive allele for colorblindness and would express the trait!
X-linked Recessive Inheritance b Example #2: Hemophilia Hemophilia Hemophilia b Hemophilia is a serious ailment in which the blood lacks a clotting factor, and therefore when an individual is injured, they cannot stop bleeding. b Hemophilia is also controlled by recessive alleles on the X chromosome.
Try this problem b b A woman who is heterozygous (a carrier) for hemophilia marries a normal man: b b a. What are the genotypes of the parents? b b b. Make a Punnett square for the above cross. b b c. What is the probability that a male offspring will have hemophilia? __________ b b d. What is the probability of having a hemophiliac female offspring? _________
X-linked Dominant Inheritance b X-linked dominant traits are traits that result from the presence of a dominant allele on the X chromosome. b Unlike X-linked recessive traits, females and males both require only ONE dominant allele in order to express the trait. b X-linked dominant traits are represented by an X, superscript capital letter or a (+)
X-linked Dominant Inheritance b Example: Faulty Tooth Enamel and Dental Discoloration b Individuals who have an X chromosome that carries a dominant allele for this trait will have dental discoloration.
Try these problems! b Would a heterozygous woman for dental discoloration display the trait? YES! Because this is a X-linked dominant trait, you only need to carry one dominant allele in order to express the trait.
Try these problems! b What percentage of the children from a heterozygous mother and an affected father would have dental discoloration? b Represent dental discoloration with a “D” All of the daughters will display the trait as they each carry at least one dominant allele. One son will demonstrate the trait while the other won’t.
Y-linked Inheritance b Y-linked traits are controlled by alleles on the Y chromosome b Another word for Y-linked traits is holandric traits as they are “wholly male”.
Y-linked Inheritance b Do the words homozygous or heterozygous apply to Y-linked traits? b Are females affected by Y-linked traits? No, because there is only ever one Y chromosome present at a time! No, because females don’t carry Y chromosomes!
Y-linked Inheritance b An example of a Y-linked trait is..... HAIRY EARS!
Y-linked Inheritance b All of the sons of an affected male will display this Y-linked trait.
A final example of Sex-linked Traits b Eye color in fruit flies ( Drosophilia melanogaster ) b Eye color is controlled by the X chromosome. b Red eyes are dominant to white. b White eyes are most common in males. b Females only display white eyes if they are homozygous recessive for the trait.
Fruit Flies Continued b What type of X-linked inheritance is this? b 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!
Let’s Try These b Problems Problems b Practice Problems Practice Problems Practice Problems