11 - Genotype And Phenotype

Question 1

What are the two main things that affect a phenotype?

Answer 1

• Environment and the genotype

Question 2

What is the SRY gene?

Answer 2

The gene that codes for male development on the Y chromosome

Question 3

Who has the ‘secret ginger’ gene?

Answer 3

Everyone!! Everyone has the same genes but different alleles.

Each person has two alleles

Question 4

What is homozygous, heterozygous and hemizygous?

Answer 4

Homo - Two of the same alleles for a gene

Hetero - Two different alleles for a gene

Hemi - Only one allele of a gene (e.g males X and deletion)

Question 5

What is a dominant allele?

Answer 5

Determines the phenotype

Question 6

How do you determine which gene is dominant by looking at genotype?

Answer 6

You can’t, you have to look at the phenotype

Question 7

What is co-dominance and give an example of where this occurs?

Answer 7

Where two alleles are equally dominant, both expressed in the phenotype

In the blood isoglutamin gene codes for glycoproteins on RBC surface. A and B dominant over O but A and B are codominant

Question 8

What is the genotype of blood phenotypes A, AB, O

Answer 8

- A: I^aI^a or I^aI^o

- B: I^bI^o or I^bI^b

^- O: I^oI^o (no glycoproteins)

Question 9

What are the rules to drawing a pedigree diagram?

Answer 9

Question 10

What are the different types of inheritance patterns?

Answer 10

- Autosomal (recessive, dominant, polygenic ^{(multiple genes)}, complex^environment)

- Sex linked/ Mendelian (X-linked recessive, X-linked dominant, Y linked)

Question 11

What are the common themes with autosomal recessive genes and an example of a disease this gene can cause?

Answer 11

• All heterozygotes unaffected but are carriers
• Disease can skip generations
• Males and females equally affected

CYSTIC FIBROSIS AND SICKLE CELL ANAEMIA

Question 12

What are the characteristics of an autosomal dominant gene and an example of a disease caused by this gene?

Answer 12

• All heterozygotes affected
• Rarely found homozygous as unlikely to survive so assume patients are heterozygous with autosomal dominant
• Cannot skip generations, have to have affected parent
• Males and females equally affected

HUNTINGTONS DISEASE AND MARFANS

Question 13

What are the characteristics with X-linked recessive genes and what is an example of a disease caused by this?

Answer 13

• Hemizygous males and homozygous females affected
• More common in males
• Male cant give trait to son
• Heterozygous mother has 50% chance of son being affected
• Homozygous mother will have affected son
• Affected female will have affected father and at least carrier mother

HAEMOPHILIA A

Question 14

What do you need to remember when drawing sex-linked genes punnet squares?

Answer 14

Right it like X^A Y

Question 15

What are the common characteristics of an X-linked dominant gene and what is a disease caused by this gene?

Answer 15

• Hemizygous males and heterozygous females affected
• Affected males cannot give the disease to their sons

FRAGILE X

Question 16

What are some Y linked disorders and some characteristics of the gene

Answer 16

• Hemizygous
• Only affects males
• Hairy ears
• Y-chromosome infertility (can’t produce fertile sperm due to deletions on y-chromosome after fertilisation. if use reproductive assitance techniques all boys will have issue)
• Swyer syndrome (XY but female genitals)

Question 17

What is Swyer syndrome?

Answer 17

• An individual has XY karyotype but they have female genitilia and streak gonads so if left untreated they won’t go through puberty

Question 18

What are mitochondrial disorders?

Answer 18

All inherited from mother so an affected mother will have all affected children. If affected father has children his children will be fine

Question 19

What is the genetic pattern of albinism?

Answer 19

Polygenic recessive, e.g 2 albino parents could have a normal child as polygenic

Question 20

Why are genes that are linked important to look at?

Answer 20

Disorder may be polygenic but as on same chromosome they will go through independent assortment together in meiosis so likely to both be inherited.

Phenotypic ratio will not be 1:1:1:1 like non-linked

If linked and far apart on chromosome more likely to appear 1:1:1:1 ratio as higher recombination frequency

Question 21

If trying to work out the probability that a grandchild will have a disease what do you do?

Answer 21

Multiply the chance of child getting it by chance of their child getting it from them

e.g 0.5²

Question 22

When looking at a pedigree diagram of an X-linked recessive disease how should you go about working out the genotypes?

Answer 22

• Start at the bottom
• Work out males first
• Some females you can’t know their genotype for certain
• If any recombination must be due to mother during oogenesis

Question 23

How can you work out the recombination frequency in a family and can these frequency be used for different families?

Answer 23

• Look at the people who’s genotype you know for certain (usually males whos genotype you know)
• Count how many have recombination and write it as a fraction out of all the individuals
• Can be applied to every family as genes are in same position on everyones chromosomes so linked the same and likely to have same recombination frequency

Question 24

What is important to take into consideration when deciding if someone’s child is going to be a carrier or not?

Answer 24

• Need to take into consideration the recombination frequency