11 - Genotype And Phenotype Flashcards
What are the two main things that affect a phenotype?
- Environment and the genotype
What is the SRY gene?
The gene that codes for male development on the Y chromosome
Who has the ‘secret ginger’ gene?
Everyone!! Everyone has the same genes but different alleles.
Each person has two alleles
What is homozygous, heterozygous and hemizygous?
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)
What is a dominant allele?
Determines the phenotype
How do you determine which gene is dominant by looking at genotype?
You can’t, you have to look at the phenotype
What is co-dominance and give an example of where this occurs?
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
What is the genotype of blood phenotypes A, AB, O
- A: IaIa or IaIo
- B: IbIo or IbIb
- O: IoIo (no glycoproteins)
What are the rules to drawing a pedigree diagram?
What are the different types of inheritance patterns?
- Autosomal (recessive, dominant, polygenic (multiple genes), complexenvironment)
- Sex linked/ Mendelian (X-linked recessive, X-linked dominant, Y linked)
What are the common themes with autosomal recessive genes and an example of a disease this gene can cause?
- All heterozygotes unaffected but are carriers
- Disease can skip generations
- Males and females equally affected
CYSTIC FIBROSIS AND SICKLE CELL ANAEMIA
What are the characteristics of an autosomal dominant gene and an example of a disease caused by this gene?
- 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
What are the characteristics with X-linked recessive genes and what is an example of a disease caused by this?
- 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
What do you need to remember when drawing sex-linked genes punnet squares?
Right it like XA Y
What are the common characteristics of an X-linked dominant gene and what is a disease caused by this gene?
- Hemizygous males and heterozygous females affected
- Affected males cannot give the disease to their sons
FRAGILE X
What are some Y linked disorders and some characteristics of the gene
- 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)
What is Swyer syndrome?
- An individual has XY karyotype but they have female genitilia and streak gonads so if left untreated they won’t go through puberty
What are mitochondrial disorders?
All inherited from mother so an affected mother will have all affected children. If affected father has children his children will be fine
What is the genetic pattern of albinism?
Polygenic recessive, e.g 2 albino parents could have a normal child as polygenic
Why are genes that are linked important to look at?
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
If trying to work out the probability that a grandchild will have a disease what do you do?
Multiply the chance of child getting it by chance of their child getting it from them
e.g 0.52
When looking at a pedigree diagram of an X-linked recessive disease how should you go about working out the genotypes?
- 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
How can you work out the recombination frequency in a family and can these frequency be used for different families?
- 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
What is important to take into consideration when deciding if someone’s child is going to be a carrier or not?
- Need to take into consideration the recombination frequency
