Chapter 17 - Inherited change Flashcards
What is a phenotype
The expression of the genotype (genetic constitution) and its interaction with the environment
The phenotype is influenced by both genetic makeup and environmental factors.
What is a genotype
The genetic constitution of an organism
The genotype determines the potential traits of an organism.
Define a gene.
The base sequence of DNA at a particular locus, that codes for the amino acid sequence of a polypeptide (and a functional RNA)
Genes are the fundamental units of heredity.
What is an allele
A different form of a gene
Alleles can be dominant or recessive.
What are homologous chromosomes
A pair of chromosomes (one maternal, one paternal) with the same genes at the same loci
Homologous chromosomes carry the same types of genes but may have different alleles.
What does locus refer to
The fixed position a gene occupies on a particular chromosome
Each gene has a specific location on a chromosome.
What is a dominant allele
Always expressed in the phenotype when present
Dominant alleles mask the expression of recessive alleles.
What is a recessive allele
Only expressed in the phenotype if both alleles are recessive
Recessive alleles require two copies to be expressed.
What does heterozygous mean
When there are two different alleles present
Heterozygous individuals have one dominant and one recessive allele.
Define homozygous
When the alleles are the same
Homozygous can be either dominant or recessive.
What is homozygous dominant
When both alleles are dominant so the phenotype is the dominant characteristic
Homozygous dominant individuals will always express the dominant trait.
What does homozygous recessive mean
When both alleles are recessive so the phenotype is the recessive characteristic
Homozygous recessive individuals express the recessive trait.
What is a diploid organism
Two sets of chromosomes – usually found in body cells
Diploid organisms have pairs of homologous chromosomes.
Define haploid
One set of chromosomes - gametes
Haploid cells are produced during meiosis.
What is monohybrid inheritance
The inheritance of a single gene
Monohybrid crosses examine the inheritance of one trait.
What does pure-breeding refer to
Homozygous organisms
Pure-breeding individuals produce offspring with the same traits.
What is the F1 generation?
First filial generation of offspring
The F1 generation results from a cross between two parental (P) generation organisms.
What is a Punnett Square
Diagram used to show combination of alleles in a genetic cross
Punnett Squares help predict the genotypes of offspring.
What is monohybrid inheritance
Monohybrid inheritance is the inheritance of a single gene, coding for a particular characteristic
What are the steps in making a genetic cross
- Assign a letter for the characteristic (usually the first letter of the feature e.g. G for green pods). Upper and lower case letters should be different in appearance. Write a key for the letter you are using.
- State the parental phenotype.
- State the parental genotype.
- State the parental gametes (in circles).
- Draw and complete a Punnett square to show possible outcomes of the genetic cross. Label the axes with sex of parent corresponding to those gametes.
- State the F1 genotype, either in a ratio, or a % for each option.
- State the F1 phenotype, either in a ratio, or a % for each option.
example diagram for a genetic cross
How are ratios used in genetics
- Allow us to compare offspring phenotypes, and genotypes
- Follow instructions in question – e.g. male : female would be different to female : male
- Divide both sides by the same value so it ends up x : 1, unless it states otherwise
- Include information about the phenotype or genotype in your answer
What is Dihybrid inheritance
Inheritance of two characteristics, determined by two genes, usually on separate chromosomes (unlinked)
example: eye colour or hair colour
example of dihybrid inheritance genetic cross
What is codominance
- when both alleles are expressed in the phenotype
- both alleles are equally dominant
example: of codominance with snapdragon flower colour
alleles are for red flowers and white flowers
white = non-functioning enzyme
if red and white alleles occur together, phenotype is pink flower
pink = enough enzyme for a bit of red colouring so seen as pink
example of genetic cross showing codominance
What is different about multiple alleles coding for one protein
when more than two alleles code for a single gene but there are only ever 2 alleles present at a time (second allele should be in superscript)
Allele Iᴬ – codominant, leads to production of antigen A
Allele Iᴮ – codominant, leads to production of antigen B
Allele Iᴼ – recessive and neither A or B antigens produced
example of a genetic cross showing codominace in blood types
What is sex linkage
when a gene is carried on a sex chromosome (X or Y)
features of sex chromosomes
- Females = XX
- Males = XY
- Males always receive X from mother and Y from father
- Non – homologous as Y chromosome is shorter than X chromosome
- Non - homologous section is not present on Y chromosome
- If an allele for a gene is on the non – homologous section of X, that will be the phenotype (because the other allele is not present)
inheritance of sex-linked conditions
- If a recessive genetic disorder is sex-linked and carried on the non - homologous part of the X chromosome, it may have a higher frequency in males
- It will not have a corresponding allele on the Y chromosome
- The phenotype can therefore only be recessive
On homologous chromosomes, the second allele could be dominant so this would lead to a dominant phenotype - Only females can pass on X-linked characteristics to male offspring, as only females pass on the X chromosome to male offspring
example of a genetic cross showing the inheritance of sex linked genetic disorder
