Inheritance Flashcards
What is a genotype?
Genetic make up of an organism.
ALL the alleles that an organism has.
What is an allele?
Different versions of a gene found at the same locus on a chromosome.
What is a gene?
Short section of DNA that codes for a single polypeptide
What is a phenotype?
Observable or biochemical characteristics of an organism.
Expression of the genotype and its interaction with the environment.
What is a homologous chromosomes
A pair of chromosomes matched in shape and size, which contain the same genes.
Formed when haploid gametes fuse to make zygote at fertilisation
Locus
Position of a gene on a chromosome
Homozygous
Two alleles at a gene locus are the same
Heterozygous
Two alleles at a gene locus are different
Dominant allele
The allele of the heterozygote that is expressed in the phenotype
Recessive allele
The allele that is only expressed when homozygous. It is not expressed when a dominant allele is present.
A dominant allele is …
Where both alleles are expressed in the phenotype
What are multiple alleles?
There are more than two alleles for a particular gene
In a diploid human cell how many chromosome pairs are there?
23
In meiosis, what happens to the diploid number?
It becomes haploid.
It halves
Characteristics are determined by your allele combinations. How many alleles for each characteristic are present in a gamete?
1
Pure breeding plants are said to be …
Homozygous
What is the difference between monohybrid inheritance and dihybrid inheritance?
Monohybrid - inheritance of a SINGLE gene
Dihybrid - inheritance of TWO genes (that are located on different chromosomes)
Give an example of a characteristic that involves multiple allelles
Blood groups
Identify the chromosomes that determine sex
X and Y
In most organisms XX = female and XY = male
When might you use a Chi squared test?
Sample size is large (20+)
Data falls int categories
Compare experimental observations with theoretical/expected ones.
When performing a statistical test what must you always state before you carry out the test?
Null hypothesis
There is no significant difference between …. and …
What are autosomes?
The chromosomes that are not the sex chromosomes. In humans there are 22 pairs of autosomes.
What is meant by autosomal linkage?
Two (or more) genes are carried on the SAME chromosome
For autosomal linkage what do we have to assume?
There is no crossing over
Genes remain together during meiosis
What is epistasis?
The allele of one gene affects or masks the expression of another allele in the phenotype
What phenotypic ratio would you expect for a monohydrid cross between two heterozygous individuals?
3:1
3 dominant : 1 recessive
What phenotypic ratio would you expect for a dihybrid cross between two heterozygous individuals?
9:3:3:1
A carrier is ….
A person in possession of an allele that is not expressed in the phenotype
What phenotypic ratio would you expect for codominant cross between 2 heterozygotes?
1:2:1
Sometimes you do not get expected phenotypic ratios because …
Small sample size
Autosomal linkage
Epistasis
Name a sex linked condition
Haemophilia
Colour blindness
A characteristic is said to be sex linked when …
Its is carried on the sex chromosomes
How can you tell from a pedigree chart if a condition is sex linked.
Males will only be affected
Why are males more likely to express recessive traits of sex linked conditions?
Only have 1 copy of X chromosome
No second allele to mask a recessive one
How are X and Y chromosomes different?
X is bigger/contains more genes
Y is smaller/contains fewer genes
When might genes that are present on the same chromosome NOT be inherited together?
Crossing over in meiosis I
The closer together 2 genes are the more closely linked they are - why?
Crossing over is less likely to split them up
If two genes are said to be linked what does this mean?
They are on the same chromosome
What is meant by codominant alleles?
Two dominant allleles that both contribute to the phenotype, by showing a blend of both characteristics or the characteristics appearing together.
A woman has the blood group O. Give her genotype.
XX Io Io
A male has blood group AB. Give his genotype
XY IA IB
