10.2 Inheritance Flashcards
How do unlinked genes segregate as a result of meiosis?
Unlinked genes segregate independently as a result of meiosis
What is segregation?
The separation of the two alleles of every gene that occurs during meiosis
What is independent assortment?
The observation that the alleles of one gene segregate independently of the alleles of other genes
Where can unlinked genes be found?
On different chromosomes
How do unlinked genes segregate?
Independently as a result of meiosis
Where can linked genes be found?
On the same chromosome
How do linked genes segregate?
They do not segregate independently
What is the exception for linked genes to be segregated independently?
If they are far apart on the chromosome
What does it mean when two gene loci are further apart on a chromosome?
There is a greater chance of recmobinant gametes forming
When are gene loci said to be linked?
If they are on the same chromosome
What is a locus of a gene?
A particular gene that is found in a specific position on one chromosome type
What does it mean when two chromosomes are homologous?
They have the same sequence of genes
How are homologous chromosomes not usually identitical to each other?
Because, for at least some of the genes on them, the alleles will be different
What are autosomes?
Chromosomes that are common to males and females
* In males there is an X and another is a Y chromosome.
* In female two of them are X chromosomes
* The other 6 chromosomes are common to both male and females <- they are called autosomes
What are autosomes?
Chromosomes that are common to males and females
* In males there is an X and another is a Y chromosome.
* In female two of them are X chromosomes
* The other 6 chromosomes are common to both male and females <- they are called autosomes
What are the two types of linkage?
- Autosomal gene linkage
- Sex linkage
What is autosomal linkage?
When the genes are on the same autosome
* gene loci present on the same autosome (non-sex chromosome) that are often inherited together
What is sex linkage?
When the genes are located on the X chromosome
What can variation be? (2)
Discrete or continuous
What is referred to as variation?
The differences between individual organisms
Is blood type discrete or continuous variation?
Discrete because while there are several blood types, there are no in-between categories
Is blood type discrete or continuous variation?
Discrete because while there are several blood types, there are no in-between categories
What type of variation do the phenotypes of polygenic characteristics tend to show?
Continuous variation
What is an example of continuous variation?
Height
What does a normal distrubution curve look like?
A bell-shaped curve
What are 4 characteristics of a normal distribution?
- The mean, mode and median are the same
- The distribution has a characteristic bell shape which is symmetrical about the mean
- 50% of the values are less than the mean and 50% are greater than the mean
- Most values lie close to the mean value - the number of individuals at the extremes are low
What are polygenic traits?
Traits that are controlled by two or more than two genes (usually by many different genes) at different loci on different chromosomes
* These genes are described as polygenes
What is polygenic inheritance?
Polygenic inheritance refers to a single characteristic that is controlled by more than two genes (also called multifactorial inheritance) Polygenic inheritance patterns normally follow a normal (bell-shaped) distribution curve - it shows continuous variation.
What are the two causes of variation?
Genetic and environmental
What are 3 causes of genetic variation?
- Mutations - changes to the DNA sequence that lead to new alleles
- Meiosis - independent assortment and crossing over
- Sexual reproduction - random fusion of gametes from two unrelated individuals
What are characteristics that exhibit discontinuous variation usually determined by?
the alleles of a single gene locus - they are monogenic
What is meant by monogenic?
Characteristics that exhibit discontinuous variation that are determined by the alles of a single gene locus
* One gene = monogenic
What is meant by polygenic?
When many genes are involved in determining such characteristics
What does it mean when the alleles have an additive effect on the phenotype?
The alleles of each gene may contribute a small amount to the phenotype, therefore the alleles have an additive effect on the phenotype
How does polygenic characteristics show continuous variation?
As a result of the additive effect on the phenotype, the phenotypic categories vary in a quantitive way.
* The greater number of gene loci contributing to the determination of the characteristic, the more continuous the variation (the greater the range)
Contintious vs discontinous variation (discrete)
How can the number and frequency of variants be predicted?
Using alternative rows of Pascal’s triangle
What may polygenic traits also be influenced by besides by multiple genes?
Environmental factors
What is variation due to polygenic inheritance tend to be?
continuous
What is an example of continious variation in humans?
Skin color
* Due to the influence of several genes
* Partially due to the environment - sunlight stimulates the production of the black pigment melanin in the skin
How is skin color an example of polygenic inheritance?
It is due to the influence of several genes
What is recombination?
The formation of a chromosome or DNA with a new combination of alleles
What is a recombinant?
An individual that has this recombinant chromosome and therefore has a different combination of characters from either of the original parents is called a recombinant
