Genetics Flashcards
How does variation occur?
Independent segregation
Crossing over
What happens during meiosis?
4 daughter nuclei produced, each with half the number of chromosome as parent cell
Who discovered genetic theory?
Gregor Mendel 1822-1884
Studied pea plants.
Discovered laws of inheritance
How is the human genome made up?
46 chromosomes
22 pairs ( autosomes)
1 pair sex chromosomes XY- male XX female
What is a gene?
Section of DNA that codes for a particular trait or characteristic
What is an allele?
A different form of a gene that codes for a different version of a characteristic
What does genotype mean?
A description of the pair of alleles present for a characteristic eg. RR
What does phenotype mean?
Physical expression of the alleles eg. Brown hair
What does homozygous mean?
Pair of alleles that produce a characteristic that are the same eg.HH
What does heterozygous mean?
Pair of alleles that produce a characteristic that are different eg. Hh
What does dominant mean?
An allele that will always be expressed even when there is only one of these alleles present (represented by capital letter)
What does recessive mean?
An allele that will only be expressed when both alleles are of this type
(Represented by lower case letter)
What are chromosomes?
Storage units of genes
What is the locus on the chromosome?
Position on a chromosome where a particular gene is found
What is a mono hybrid cross?
Cross involving a single trait eg. Flower colour
How can we calculate probability of a mono hybrid cross
Using a Punnett square
What is Mendels law of segregation?
If you have 1 allele for brown eyes(B) and one for blue eyes(b) somatic cells will have Bb and each gamete will carry 1 of B or b chosen randomly.
What is autosomal inheritance?
Inherit a recessive gene from each parent eg. Cystic fibrosis. Both parents carry gene so 1/4 chance child will get it.
What are the characteristics of autosomal recessive pedigree?
Skip a generation
Unaffected parents can produce affected child
Affected person must be homozygous
Males/females affected evenly
What are the characteristics of autosomal dominant inheritance?
Trait in every generation
Every person with the trait must have a parent with the trait
Males/ females affected evenly
Example Huntington’s disease
What does co dominance mean?
Some traits 2 alleles can be co dominant - neither allele exerts dominance over the other in the genetic hybrid.
Share dominance
Eg, blood groups and Roan cows
What is sex linked inheritance ?
The gene for a certain characteristic are carried on the sex chromosome.
Eg. Colour blindness, haemophilia, tortoiseshell cats( only in females, must have black and ginger allele.
What is incomplete dominance?
Both alleles blend their effects,eg snap dragon plants.
RW= pink flower
RR= red flower
WW= white flower
