Inherited Change Flashcards
What is genotype?
The genetic constitution of an organism. It describes all the alleles that an organism has.
What is phenotype?
The characteristics of an organism resulting from the expression of its genotype and environment
What is a gene?
A sequence of nucleotides along a short length of DNA that codes for a polypeptide
What is an allele?
An alternative form of a gene
What is homozygous?
When the alleles of a particular gene are identical
What is heterozygous?
When the alleles of a particular gene are different
What is recessive?
Two copies of the allele needed for the characteristic to be expressed in the phenotype
What is dominant?
Only one copy of the allele needed for the characteristic to be expressed in the phenotype
What is co-dominance?
Where both alleles contribute to the phenotype
What is a test cross?
A particular type of cross when an organism of unknown genotype is crossed with a homozygous recessive organism.
It can determine whether an organism is homozygous or heterozygous dominant
Blood type A
- cannot have B or AB blood (anti-b antibodies)
- can have A or O
- antigen A and anti-b antibodies
Blood group B
- cannot have A or AB blood
- can have B or O
- antigen B and anti-a antibody
Blood group AB
- can have any type of blood, is the universal recipient
- has no antibodies to react with A or B
- has antigens A+B and no antibodies
Blood group O
- can have only O blood
- is universal donor
- no antigens and both antibodies
- no antigens for the recipients immune system or reaction against
What is sex-linkage?
A gene is described as being sex-linked if it is found on one of the sex chromosomes
What are the sex chromosomes?
- females: XX
- males: XY
Where do sex chromosomes come from?
- Y chromosomes only come from the father
- X from mother (and father)
Why are characteristics from recessive alleles more common in males?
- controlled by recessive alleles on non-homologous portion on the X chromosome will appear more frequently in males
- this is because there is no homologous portion on the Y chromosome that might have the dominant allele
What are autosomes?
The remaining 22 pairs of chromosomes (in humans)
Apart from sex chromosomes
What is autosomal linkage?
If two or more genes are carried on an autosome
What is different about alleles when they are autosomally linked?
They don’t segregate according to independent assortment
When is crossing over least likely to occur on autosomally linked chromosomes?
When the genes are closest together
What is epistasis?
- arises when the allele of one gene affects/masks the expression of another in the phenotype
How can epistasis occur for enzymes?
- if recessive alleles code for non-functional proteins, then the pathway may not be completed
- the effects of the enzyme cannot be expressed because no pigment can be made
What is recessive epistasis?
- two alleles for the masking epistasis gene must be present and so the genotype of the other gene becomes irrelevant
What is dominant epistasis?
- the presence of at least one epistasis gene masks the effect of the other gene which becomes irrelevant
Why do the results of genetic crosses often differ from predicted results?
- crossing over
- random fertilisation
- independent segregation
How many different gametes can be produced by meiosis from a cell?
- 2 to the power of how mean sets of genes there are
What is the nature of multiple alleles?
- genes may have more than one allele e.g. blood group
- although there maybe multiple possible alleles- only 2 can be present in an individual (2 homologous chromosomes)
