Genetics- Patterns of Inheritance Flashcards
What are the causes of genetic variation?
- Genetic differences
- Environmental influences
- Usually a combination of both
Features of continuous variation:
- Normal distribution curve
- Polygenic inheritance
- Environmental influences
Features of discontinuous variation:
- Mostly genetic
- Controlled by alleles of one gene or a very small number of genes
- Qualitative
- Small number of distinct classes or categories
What are the causes of genetic variation?
-Independent assortment
-Crossing over
-Mutations
-Random Fertilisation
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What is the Mendelian ratio for a monohybrid cross?
3:1
What is the Mendelian ratio for a dihybrid cross?
9:3:3:1
What is Epistasis?
Occurs when there are multiple alleles of two or more genes interacting with one another to control one phenotypic trait. The presence of one genes suppresses the expression of another gene
What is a hypostatic gene?
One that is suppressed
What is an epistatic gene?
Gene that suppresses the expression of another
How does crossing over cause genetic variation?
In Prophase I, sections of DNA on sister chromatids become entangled and break off and rejoin, resulting in exchange of DNA. This means that new combinations of alleles are created.
How does independent assortment create variation?
During metaphase I, the chromosomes line up on the metaphase plate in random order, independently of each other. This can result in many different combinations of alleles facing the poles of the cell so when it divides, each cell contains varied genetic information
How does random fertilisation create variation?
Gametes contain different alleles for genes therefore when gametes fuse, new combinations of alleles are formed. Also, multiple sperm compete to fuse with the egg so any combination can be created this way.
How do mutations create variation?
Changes in base sequence means that bonds are broken and reformed changing the specific 3D tertiary shape. This means that proteins may not be able to carry out their function therefore affecting the phenotype.
What does the Chi-squared test?
Measures the size of difference between the results you get and those expected, and whether that difference is significant or not.
How to work out expected number for Chi Squared test?
Total number x ratio of each phenotype
What is polygenic inheritance?
A single phenotype is controlled by two or more genes at different loci
What does the recombination frequency measure?
The amount of crossing over that has happened in meiosis
Recombination frequency equation:
Number of recombiant offspring/Total number of offspring x100
What can the recombination frequency be used for?
Recombination frequency for a number of characteristics coded for by genes on the same chromosome can be used to map the genes on the chromosome. RF of 1% relates to a distance of one map unit on a chromosome
What is co-dominance?
Both alleles are dominant and expressed in the phenotype. Alleles are independent and the phenotype results from full expression of both alleles
Why is blood group an example of co-dominance?
Both A and B are co-dominant over O.
What is the Rhesus factor?
People who are rhesus positive have antigen D on their RBC. R+ is dominant over R-
How is sex determined?
23rd pair of chromosomes in humans are the sex chromosomes, which are both different. Females have two X chromosomes while males have one X and one Y chromosome. The Y chromosome only contains a gene which will cause the embryo to develop as a male. Therefore, the sex of the offspring is determined by whether the sperm fertilising the egg contains an X or Y chromosome
What is sex-linkage?
Some characteristics are determined by genes carried on sex chromosomes. As the Y chromosome is much smaller than the X chromosome, there are a number of genes that males do not have a copy of. Therefore, any characteristic caused by a recessive allele on the section of the X chromosome, which is missing in the Y chromosome, will occur more frequently in males. Females, however, will often have a dominant allele present in their cells