Chapter 17 - Inherited Change Flashcards
What do the terms gene and allele mean?
Gene - a section of DNA that codes for a specific protein
Allele - a specific version of a gene
What do the terms phenotype and genotype mean?
Phenotype - visible characteristics of an organism (determined by genotype and environment)
Genotype - genetic composition of an organisms (combination of alleles found)
What do the terms dominant and recessive mean?
Dominant - alleles always visible in phenotype of an organisms if present on gene
Recessive - allele only visible in phenotype if in presence of another identical allele
What do the terms homozygous and heterozygous mean?
Homozygous - alleles for a particular gene are identical (GG,gg)
Heterozygous - alleles for a particular gene are different (Gg)
What does it mean to have multiple alleles? Provide an example
When a gene has more than 2 alleles
- e.g. Four blood groups - A, B, AB, O
What does the term co-dominance mean? Provide an example
When both alleles contribute to/are expressed in phenotype
E.g. white cow coat and red cow coat = both shown creating roan coat
What is monohybrid inheritance?
Looking at inheritance of a single gene + controlling a single characteristic
What was the example for monohybrid inheritance?
Pea Pod Colour
GG or Gg = green pod
gg = yellow pod
What are the rules applied to monohybrid inheritance for 2 homozygous parents
When two homozygous parents are combined
- In F1 GENERATION - all offspring will be heterozygous and show dominant phenotype
- in F2 GENERATION - will be a 3:1 ratio
What are the chromosomal pairs for females and males?
Females = XX (homologous)
Males = XY (not homologous) - as Y is smaller
What does it mean for something to be sex linked?
Any gene that is on the X or Y chromosome is said to be sex-linked
What’s the key idea relating to sex linked diseases?
Going to be more common in males than females because they only need one allele to then show disease
- as only have one X chromosome which the gene is on
- females can be carriers but don’t show in phenotype
When a male and female cross, what is the ratio produced?
1:1
50% male and 50% female
What is haemophilia?
A genetic blood clotting disorder
Where is the gene for haemophilia located?
Gene for factor VIII (protein involved in blood clotting) is located on X chromosome
What are the dominant and recessive alleles for haemophilia?
X^H - functional factor VIII allele (healthy)
X^h - factor VIII doesn’t produce
What are pedigree charts used for + list the symbols for:
Males
Females
Presence of characteristic or not
Used to trace inheritance of sex-linked characteristics
Males - represented by a square
Female - represented by a circle
Presence of characteristic - represented by shading in shape
What is dihybrid inheritance? Give an example
Inheritance of two characteristics, determined by two different genes on different chromosomes at the same time
Seed colour - yellow or green
Seed shape - round or wrinkled
= yellow and wrinkled or yellow and round
= green and wrinkled or green and round
What are the rules associated with dihybrid crosses?
- Homozygous dominant with recessive homozygous
- 2 heterozygous
- Heterozygous with recessive homozygote
- if crossing a homozygous dominant parent with a recessive homozygous - all offspring will be heterozygous and have dominant phenotype
- if crossing 2 heterozygous offspring = 9:3:3:1 ratio
- if crossing a heterozygote with recessive homozygote = 1:1:1:1 ratio
What is epistasis?
It occurs when 2 genes (usually on different chromosomes) interact together to affect the phenotype
- an allele of one gene may affect or mask expression of another gene
What is chi-squared?
A statistical analysis test used to evaluate whether the difference between observed and expected data is statistically significant
- always begins with a null hypothesis + mainly used for categorical data
What is the equation for chi-squared?
(observed-expected) ² / expected
How is the degree of freedom worked out?
Number of categories - 1
What does it mean in the following scenarios?
- When chi-squared < critical value
- When chi-squared > critical value
- When chi-squared is less than critical value - you can accept the null hypothesis as there is no significant difference between observed and expected showing it is due to chance
- When chi-squared is more than critical value - you can reject the null hypothesis as there is a significant difference between observed and expected showing it is not due to chance
What is autosomal linkage?
Still dihybrid inheritance (two separate genes)
Can be:
- linked = two genes found on same chromosome
- unlinked = two genes occur on separate chromosomes
In unlinked genes, how many potential gamete combinations are there?
AaBb
4 - AB, Ab, aB, ab
When two heterozygous unlinked genes are crossed what ratio of offspring is produced?
AaBb x AaBb
9:3:3:1 ratio
- due to independent segregation
In linked genes, how many potential gamete combinations are there?
AB on one autosome
ab on another autosome
2 - AB and ab
What ratio is produced when the two gamete combinations are crossed in linked genes?
AB//ab x AB//ab
= 3:1 ratio (if no crossing over)
What needs to be mentioned if:
a question asks you to explain the results of numbers of offspring that clearly show genes are linked…
- State which alleles are linked eg. usually dominant and recessive AB and ab
- State what gametes the parents will therefore mainly produce
- State that crossing over produces few of the other gametes (state what they are) eg. Ab and aB
- State that therefore that’s why you have a high number of offspring (eg. the phenotypes that there are many of) and very few offspring (eg. the phenotypes that there are very few of)
