Section 7 - Chapter 17: Inherited Change - old Flashcards
Why do we resemble our parents but are not identical?
- Inherit alleles/ genes from both parents. Fusion of gametes. Gametes are haploid.
- When egg/sperm meet we have 2 copies of each gene
- Some are dominant and recessive.
What is a gene?
Short section of DNA on a chromosome, this is a sequence of nucleotide bases that code for a specific protein.
What is an allele?
Different forms/versions of a gene
What is the genotype?
The genetic constitution of an organism. Combination of alleles. e.g Bb. Can be influenced by environment/mutations
What is the phenotype?
Observable or biochemical characteristics of an organism due to genotype/allele and the environment
What does homozygous mean?
Where 2 alleles for a given gene are the same ( BB)
What does heterozygous mean?
Where 2 alleles for a given gene are different (Bb)
What does dominant allele mean
A dominant allele is always expressed in the phenotype
What does recessive allele mean?
An allele that influences the phenotype if 2 copies are present
What is codominance?
When 2 alleles have equal influence in the phenotype.
Phenotype can be a blend of both alleles (colour) or both features are represented separately (Blood Group)
What did Mendel discover when he crossed tall and dwarf pea plants
- The gene that controls height in pea plants has 2 alternative forms called alleles
- The allele for tallness is dominant and allele for shortness is recessive.
What are dihybrid crosses used
Shows how 2 characters determined by 2 different genes located on different chromosomes are inherited.
What are multiple alleles
Where there are more than 2 alleles of which only 2 may be present at the loci of an individual’s homologous chromosomes
e.g blood group
How many pairs of chromosomes do humans have
23 pairs
What is the 23rd pair also known as and what are they for male and female
- 23rd pair is the sex determining chromosomes
- XX is female and XY is male
Any gene that is carried on either X or Y chromosome is said to be …. and which is longer
- Sex-linked
- The X chromosome is longer and for most of the chromosome there is no equivalent homologous portion to match with the Y chromosome.
What is haemophilia
- Defective gene on the x chromosome
- Blood clots slowly and internal bleeding
- Affected individuals have a mutated allele (recessive) which results in a non-functional protein
Exam Question : Male fruit flies are more likely to show a phenotype produced by a recessive allele carried on the X chromosome. Explain why
As males have only 1 X chromosome they only need 1 recessive allele to show the phenotype however females must present 2 recessive alleles as they have 2 X chromosomes.
Exam Question: During meiosis, when the X and Y chromosome pair up they dont form a typical bivalent. Explain why
X and Y chromosomes are different sizes so chromatids are unable to line up and form bivalent/ only short pairing region/ most of length not homologous.
Couple 1 and 2 have the disorder and have 3 children in which 1 doesn’t have the disorder. How can you tell the disorder is caused by a dominant allele.
The couple have a son that doesnt have the disorder whilst they do.
They therefore must be heterozygous and as they have the disorder it must be dominant.
Couple 3 and 4 dont have the disorder but their daughter does. How can you tell the condition is caused by a recessive allele.
3 and 4 dont have the disorder but their daughter does therefore they must be carriers and passed on their recessive alleles.
In fruit flies, the genes for body colour and wing length are linked. Explain what this means
The genes are on the same chromosome
What are the remaining 22 chromosomes (not sex determining) called and what is the name when genes are located on the same autosome.
- Autosomes. The name given to the situation where 2 or more genes are carried on the same autosome is called autosomal linkange
Why are the ratios of 2 phenotypes more than others in autosomal linkage
- Linked genes remain together during meiosis and therefore remain together when they pass into the gamete.
- Small numbers in other phenotypes are due to crossing over.
Distinguish between sex-linkage and autosomal linkage
- In sex linkage the linked genes are on the same sex chromosome whereas in autosomal linkage they are on any chromosome other than the sex chromosomes.
What is epistasis and give an example
- Epistasis arises when the allele of 1 gene affects or masks the expression of another in a phenotype. Coat colour in mice.
What is a species
A group of similar organisms that can reproduce to produce fertile offspring
What is a species
A group of similar organisms that can reproduce to produce fertile offspring
What is a population
A group of organisms of the same species that occupies a particular area at the same time
What is a Gene Pool
All the alleles of all the genes of all the individuals in a population
What is Allele Frequency
Number of times a particular allele occurs within the gene pool (Usually given as a % or decimal)
What is the Hardy Weinberg Principle
- Predicts the frequencies of alleles in a population won’t change from generation to generation
- Assumption that proportion of dominant and recessive alleles remain the same from generation. 5 conditions need to be met.
What are the 5 conditions that mean Hardy Weinberg Principle can be used.
- There is no selection - all alleles are equally likely to be passed on
- No mutations take place
- There is a large population
- Mating within the population is random
- No emigration/ immigration - no alleles enter or leave the population
What can the 2 Hardy Weinberg equations be used for
- Estimate the frequency of particular alleles
- Test whether or not the HW principle applies to particular alleles - to test whether other factors affect allele frequencies.
What is the equation for allele frequency
- p+q = 1, p= frequency of dominant allele. q = recessive allele.
- The total frequency of all the possible alleles for a characteristic in a population is 1.0.
What is the equation for genotype frequency
- p2 + 2pq + q2 = 1 , p2 = frequency of homozygous dominant. 2pq = heterozygous, q2= homozygous recessive.
- Total frequency of all possible genotypes. 3 genotypes.
*
