Inheritance Flashcards
What experiment did Mendel do
Pea plant experiment
What is the term to describe an organism that has the same alleles
Homozygous
From Mendel’s experiment, what number generation are the homozygous individuals in
F zero generation
From Mendel’s experiment, what is the number generation where all the individuals present the dominant gene
F 1 generation
What generation, from Mendel’s experiment have individuals that both present dominant and recessive genes
F 2 generation
When you mix 2 homozygote indiviudals (2 F zero individuals), what generation is the offspring
F one generation
If you mix 2 heterozygote individuals, what generation is the offspring
F 2 generation
What is the offspring if you mix a heterozygote and a homozygote
A non-Mendelian ratio
Define genotype
The genetic makeup of an individual / the alleles of a gene, or all of the alleles of all the genes that an individual inherits
Define phenotype
The expression of the genotypes and its interaction with the environment
Define dominant allele
The allele that is always expressed in phenotype when present
Define codominant allele
Both alleles are expressed in the phenotype when present
Define recessive allele
The allele that is only expressed in the phenotype only in the absence of a dominant allele
Define heterozygous
Possessing different alleles of genes at the same locus on homologous chromosomes
Define homozygous
Possessing the same alleles of genes at the same locus on homologous chromosomes
When writing letters for the genotype, what letter comes first
The capital letter
What is the ratio for monohybrid inheritance
3:1 (dominant: recessive)
What is the other name for the test cross
back cross
How is the test cross/ back cross carried out
- Cross dominant phenotype with a recessive phenotype
- Look at offspring
- If any offspring show recessive phenotype the dominant characteristic must be heterozygous
-If no offspring show recessive phenotype then you can’t tell
If the chi squared value is less than the critical value (@p=0.05), is the difference between the observed and expected significant and is the null hypothesis accepted or rejected
Not significant therefore is due to chance alone so accept null hypothesis
If the chi squared value is greater than the critical value @ p=0.05, is the difference between the observed and expected significant and is the null hypothesis accepted or rejected
Is significant and therefore not due to chance alone so reject null hypothesis
How do you calculate the expected value, for chi squared
(sum of observed x phenotype ratio) / sum of ratios
How do you calculate the degrees of freedom (DoF), for chi squared
number of categories (phenotypes) - 1
What are codominant alleles
Where both alleles are equally dominant and both are expressed when they are present
When writing codominant alleles into punnet squares, how do you write it
Write a gene letter, then write the colour etc, (the allele letter), like a power e.g. C^W
What is the co-dominant inheritance ratio
1:2:1
What is the other name for the sex chromosomes
Heterosomes
AQA defines any gene in this particular region to be a sex-linked gene, what is the name of the region
Non-homologous regions
What is the only chromosome that contains a non-homologous region
the X chromosome
Which chromosome is larger, the X or the Y
X
Who are more likely to have a sex-linked disease, males or females, and why
Males since they only need one recessive allele since they only have one X chromosome, wherease females have 2 X chromosomes so need 2 recessive alleles in order to have the disease
When writing the phenotype of sex-linked alleles, what must you include
The sex, female or male
When writing the genotype of a sex-linked male, what is not included and why
Whether the chromosomes are homozygous or heterozygous since only the X chromosome carries the alleles
When asked what evidence is there that this disorder is recessive from a pedigree diagram, what is the answer that you must look for in the diagram
Where an affected offspring is produced from 2 non-affected parents
When asked what evidence is there that this disorder is NOT sex linked from a pedigree diagram, what is the answer
Look for an affect daughter from a non-affected father
What is meant by the term autosomal recessive trait
Non sex chromosomes, won’t be expressed if the dominant allele is present
In a pedigree diagram what is the evidence that the disorder is sex linked
Only males have the disorder
What is the dihybrid inheritance ratio
9:3:3:1
What is autosomal linkage
The name given to the situation where 2 or more genes are carried on the same autosome
What are autosomes
Chromosomes other than sex chromosomes
In an homologous pair of autosomal linkage, how many alleles are accommodated
4
How many gametes can be produced from 1 homologous pair of linked chromosomes
2
In autosomal linkage, are most of the offspring the same or different from the parents
The same
Why in autosomal linkage, are the offspring likely to be the same as the parent
Since there are few recombinant offspring since recombinant offspring only occur if crossing over occurs
What causes recombinant offspring in autosomal linkage
Crossing over
When 2 F1 linked parents cross, how do the chromosomes act
As one
How does the degree of linkage in chromosomes vary
Depending on how close the genes are on chromosomes
If a chromosome is really linked, is it more likely to behave as one or two
one
When the chromosome is less linked, the liklihood of what increases
Likelihood of crossing over increases
Why is the likelihood of crossing over increased when the chromosomes are less linked
Since there is more space between the genes on the chromosomes, so a larger chiasma
What is epistasis
The interaction between two non-linked genes which causes one gene to mask the expression of the other in the phenotype
What is meant by the term phenotype (2 marks)
- Characteristic due to genotype
- Characteristic due to environment
In genetic crosses, the observed phenotype ratios obtained are often not the same as the expected ratios, suggest 2 reasons why (2 marks)
- Linked genes
- Random fusion of gametes
- Epistatsis
- Small sample size
- Lethal genotypes
Scientists concluded that the observed frequencies of the 4 phenotypes differed significantly from the expected frequencies. Use your knowledge of the Hardy-Weinberg principle to suggest 2 reasons why (2 marks)
- Selection
- High rate of mutation
- Immigration/ emigration
- No random mating
What is epistasis
When a gene at one locus inhibits the expression of a gene at another locus.
The alleles that are masked to the epistasic allele are said to be what
Hypostatic
What is the null hypothesis of chi-squared
‘There is no significant difference between observed and expected data, the difference is due to chance’
If the chi-squared value is greater than the critical value, do we accept or reject the null hypothesis
Reject null hypothesis
If chi-squared value is lower than critical value, do we accept or reject null hypothesis
Accept null hypothesis
Gene for eye colour is carried on the X chromosome, red is dominant, white is recessive. Explain why male fruit flies are more likely than female fruit flies to have white eyes (2 marks)
- Males have one allele;
Accept males only need one allele. - Females need two recessive alleles
OR
Females must be homozygous recessive
OR
Females could have dominant and recessive alleles
OR
Females could be heterozygous/carriers;
Mutations is one cause of genetic variation in organisms. Give 2 other causes of genetic variation (2 marks)
- Crossing over;
- Independent segregation/assortment (of homologous chromosomes);
- Random fusion of gametes
OR
Random fertilisation;
What evidence is looked for the show an allele is dominant
2 parents that both have the dominant phenotype having offspring with both the dominant and recessive. If the allele was recessive all of the offspring would then too have the recessive phenotype
What evidence it used to show that a gene is not on the X chromosome
A dominant phenotype male producing a recessive phenotype female. If the gene was on the X chromosome this would not be possible
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest 2 reasons why (2 marks)
- Small sample size;
- Fusion/fertilisation of gametes is random;
- Linked Genes;
Accept crossing over / sex linkage - Epistasis;
- Lethal genotypes;
What is meant by the term phenotype (2 marks)
- (Expression / appearance / characteristic due to) genetic constitution/ genotype / allele(s);
- (Expression / appearance / characteristic due to) environment;
What is meant by codominant alleles (1 mark)
Both alleles expressed in the phenotype (if both are present);
Explain why linked genes means
(Genes / loci) on same chromosome.
Which statistical test could be used to determine whether his observed results were significantly different form the expected results, give the reason for your choice (2 marks)
- Chi squared test;
- Categorical data.
The scientists concluded that the observed frequencies of the four phenotypes
differed significantly from the expected frequencies. Use your knowledge of the
Hardy–Weinberg principle to suggest two reasons why. (2 marks)
- Selection (against/for a blood
group/phenotype/allele); - (High rate of) mutation;
- Immigration/emigration;
- No random mating.
