Ch 15 Flashcards
(39 cards)
Hemophilia description
Hemophilia is a genetic disorder where the blood clotting process is defective. They do not make a protein that is needed for the blood to clot. It is often called “bleeders disease”.
A man without hemophilia and a woman who is a carrier for hemophilia have children.
Parent Genotypes?
X^H Y x X^H X^h
Examples of X-linked conditions
Color-blindness (c) is recessive to normal vision (C). Hemophilia (h) is recessive to being able to produce blood clotting factors (H).
Genes on the X versus Y chromosome
The X chromosome carries different genes and more genes compared to the Y chromosome.
How do Sex chromosomes determine the biological sex of an individual?
Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
If a son expresses an X-linked condition, who did he inherit it from?
Does this mean this parent also expresses the condition?
He inherited it from his mom, because mothers contribute one of their X chromosomes to their sons, which can carry sex-linked traits. His dad gave him the Y chromosome. If the condition is recessive, she may not express; she could be a carrier. But if the condition is dominant, she expresses.
The inheritance pattern of hemophilia.
Hemophilia is inherited as an X-linked recessive disorder.
When doing Punnett squares with sex-linked conditions, what must you include?
Include the X and Y chromosome with the allele written as a superscript.
Human somatic cells contain 23 pairs of chromosomes. Discuss autosomes vs sex chromosomes.
22 pairs of autosomes and 1 pair of sex chromosomes (XX or XY).
X-linked gene inheritance in males and females
When a gene is located on the X chromosome, females receive 2 copies of the gene, and males only receive 1 copy. This means females have a “backup” for each of the genes on the X chromosome, leading to more males inheriting recessive X-linked conditions.
A gene on one of the sex chromosomes is called: ________.
A SEX-LINKED gene is one that is located on a sex chromosome.
Dads pass their X chromosome to their daughters. If the daughter expresses an X-linked recessive condition, what does this tell you about her dad?
Her dad must also express it since he only has one X chromosome
Normal or wild-type dominant allele in fruit fly genetics
The normal or wild-type dominant allele is written with a “+”. Example: w+
A mutation is written with just the symbol letter. Example: w
Some of the color alleles in cats are X-linked. Study the image. Is it possible for a normal male cat to have the tortoise shell pattern?
No because he cannot be heterozygous if he is a normal male cat since he only has one X chromosome.
(He could only be tortoise shell if he had Klinefelter’s and was heterozygous, X^B X^b Y)
A normal male has what genotype and how many barr bodies?
XY, 0 barr bodies
What process/ law does the large punnett square assume
Independent assortment (the genes are assorting independently into the gametes during meiosis since the are on the same chromosome)
Exception for genes on the same chromosome
If genes are really far apart, they may appear to assort independently due to crossing over.
What does Recombination frequency tell us?
The frequency with which a single chromosomal crossover will take place between two genes during meiosis.
Recombination frequency
The number of recombinants divided by the total number of offspring, multiplied by 100.
A normal female has what genotype and how many barr bodies?
XX, 1 barr body
What is the result of crossing-over during meiosis?
Crossing-over increases genetic diversity.
Gene Separation and Mapping
The rate at which linked genes are separated can be used to produce a “map” of distances between genes. This “map” isn’t a true distance but an order of genes on the chromosome.
Alfred Sturtevant
-graduate student working in Thomas Morgan’s lab
-hypothesized that the farther apart two genes are on a chromosome, the more likely they are to be separated by crossing-over
-lead to gene maps
Use the following recombination frequencies to determine the order of the 3 genes on a chromosome:
-cn and vg recombine at a rate of 9.5%
-vg and b recombine at a rate of 17%
-b and cn recombine at a rate of 9%
The order of the genes is
b-cn-vg (this is the same as reverse order of vg-cn-b FYI).
The numbers may not be perfect since actual data was used and crossing over is random.
