3.7.1 Inheritance Flashcards
What is the genotype?
The genotype is the genetic constitution of an organism.
What is the phenotype?
The phenotype is the expression of the genetic constitution and its interaction with the environment.
What is an allele?
An allele is an alternative form of a gene.
What are the three types of alleles?
Alleles may be dominant recessive or codominant.
What does homozygous mean?
Homozygous means having two identical alleles at a specific gene locus.
What does heterozygous mean?
Heterozygous means having two different alleles at a specific gene locus.
What is a monohybrid cross?
A monohybrid cross involves the inheritance of a single gene with dominant recessive or codominant alleles.
What is a dihybrid cross?
A dihybrid cross involves the inheritance of two different genes each with dominant recessive or codominant alleles.
What is sex-linkage?
Sex-linkage refers to genes located on the sex chromosomes most commonly the X chromosome in humans.
What is autosomal linkage?
Autosomal linkage occurs when two or more genes are located on the same autosome and tend to be inherited together.
What are multiple alleles?
Multiple alleles refer to a gene that has more than two possible alleles within a population.
What is epistasis?
Epistasis occurs when the expression of one gene is influenced by another gene.
What is the chi-squared test used for in genetics?
The chi-squared test is used to compare observed phenotypic ratios with expected ratios to determine if differences are due to chance.
if a gene is sex-linked on the X chromosome, why is the phenotype more common in XY organisms? (2)
- 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;
In genetic crosses, the observed phenotypic ratios obtained in the offspring
are often not the same as the expected ratios.
Suggest two reasons why.
- Small sample size;
- Fusion/fertilisation of gametes is random;
Ignore breeding is random - Linked Genes;
Accept crossing over / sex linkage - Epistasis;
- Lethal genotypes;
What is meant by the term phenotype?
- (Expression / appearance / characteristic due to) genetic constitution
/ genotype / allele(s); - (Expression / appearance / characteristic due to) environment;
- Accept: named characteristic.
- Accept: homozygous / heterozygous / genes /DNA.
- Ignore: chromosomes.
What is meant by codominant alleles?
Both alleles expressed in the phenotype (if both are present);
In fruit flies, the genes for body colour and wing length are linked. Explain
what this means.
(Genes / loci) on same chromosome.
Mutation is one cause of genetic variation in organisms.
Give two other causes of genetic variation.(2)
1. Crossing over;
2. Independent segregation/assortment (of homologous chromosomes);
3. Random fertilisation;
in genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.
Suggest reasons why. (2)
1. Small sample size;
2. Fusion/fertilisation of gametes is random;
3. Linked Genes;
4. Epistasis;
5. Lethal genotypes;
Name the relationship between two alleles when both alleles appear in the phenotype (1)
Co-dominance
Name the type of gene interaction when one gene affected the expression of another (1)
epistasis
Which statistical test could the scientist use to determine whether his observed results were significantly different from the expected results?
Give the reason for your choice of statistical test.
(2)
1. Chi squared test;
2. Categorical data
