Section 7 - 17 Inherited change Flashcards
What did Gregor Mendel establish?
The basic laws by which characteristics are inherited from one generation to the next and how this can produce genetic variation within a population.
What is the genotype?
The genetic constitution of an organism.
Describing all the alleles that an organism has.
What does a genotype determine?
The limits within which the characteristics of an individual may vary.
What is a phenotype?
The observed or biochemical characteristics of an organism.
It is the result of the interaction between the expression of the genotype and the environment.
What factor can affect the phenotype of an organism?
The environment
What is a gene?
A length of DNA that is a sequence of nucleotide bases that normally code for a particular polypeptide.
What is a locus?
The position of a gene on a particular DNA molecule?
What is an allele?
One of the different forms of a gene.
Only one allele of a gene can occur at the locus of anyone chromosome. However, in diploid organisms, the chromosomes occur in pairs called homologous chromosomes.
What does homozygous mean?
When the allele on each of the chromosomes is the same.
What does heterozygous mean?
The two alleles are different chromosome.
What is a homozygous organism with two dominant alleles?
homozygous dominant
What is an organism where both alleles are recessive?
homozygous recessive
What does codominant mean?
When two alleles both contribute to the phenotype.
The phenotype is either a blend of both features or both features are represented.
What does it mean when a gene has more than two allelic forms?
Multiple alleles for that character
Give a step by step guide of how to represent genetic crosses
- Questions usually give the symbols to be used in which case always use the ones provided. Choose a single letter to represent each characteristic.
- Choose the first letter of one of the contracting features.
- If possible choose the letter in which the higher and lower case forms differ in shape as well as size.
- Let the higher case letter represent the dominant feature and the lower case letter the recessive one.
- Represent the parents with the appropriate pairs of letters. Lebel clearly and state phenotypes.
- State gametes produced by each parent, label and encircle.
- Using Punnett square show the results of the random crossing of the gametes. Label male, female gametes even though this may not affect the results.
- State the phenotypes of each different genotype and indicate the numbers of each type. Use higher case letter first.
What is monohybrid inheritance?
The inheritance of a single gene.
Gregor Mendel studied the colour of the pods of pea plants which come in two basic colours green and yellow
Give an example of a scientist who studied monohybrid inheritance
Gregor Mendel
Pea-plants
Explain, in detail, how Gregor Mendel investigated monohybrid inheritance
- Pea pods come in two basic colours green and yellow.
- If green pods are repeatedly bred so that they consistently give rise to plants with green pods then they are said to be pure-breeding.
- They are homozygous organisms for that particular gene.
- If a pure-breeding green-pod plant is crossed with a pure-breeding yellow-pod plant all the offspring known as the first filial or F1 generation produce green pods. This means the green pods are dominant to the allele for yellow pods which is therefore recessive.
What is the basic law of genetics?
Law of segregation
In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of alleles can be present in a single gamete.
What is dihybrid inheritance?
How two characters determined by two different genes located on different chromosomes are inherited.
What two variables did Mendle look into when investigating dihybrid inheritance?
- seed shape - round dominant to wrinkled
- Seed colour - yellow seed dominant to green.
How did Mendle investigate dihybrid inheritance?
Carried out a cross between the following two pure breeding types of plants:
- one producing round-shaped yellow seeds - both dominant
- One always producing wrinkled-shaped green seeds - both recessive
In F1 generation he obtained plants all produced round-shaped, yellow coloured seed. Then raised plants from these seeds and crossed them with one another.
4 gametes were produced.
What is the theoretical ratio for dihybrid inheritance ?
9:3:3:1
What is the theoretical ratio for monohybrid inheritance?
3:1
What was Mendel’s law of independent assortment?
Each member of a pair of alleles may combine randomly with either of another pair.
What is codominance?
Both alleles are expressed in the phenotype
What is multiple alleles?
Where there are more than two alleles of which only two may be present at the loci of an individual’s homologous chromosomes.
When does codominance occur?
Where instead of one allele is dominant and the other recessive both alleles are equally dominant.
Meaning that both alleles of a gene are expressed in the phenotype.
How can we annotate codominant cells?
Use different letters and put as superscripts on a letter that represents the gene.
What is an example of multiple alleles?
ABO blood groups.
What is the 23rd chromosome in females?
two X chromosomes
What is the 23rd chromsome in males?
One X but one slightly smaller with a different shape called Y chromosome.
What does it mean to be sex-linked?
Any gene that is carried on either the X or Y chromosome.
Give an example of a genetic disorder caused by a defective gene on the X chromosome
Haemophilia
Blood clots only slowly and there may be slow and persistent internal bleeding especially in the joints.
How rare is haemophilia?
1 in every 20,000 in Europe.
Almost entirely confined to males, in part because haemophilic females usually died with the onset of menstruation at puberty.
What is one of a number of causes of haemophilia?
A recessive allele with an altered sequence of DNA nucleotide bases that therefore codes for a faulty protein which does not function.
Results in an individual being unable to produce a functional protein that is required in the clotting process.
Give an example of a useful way to trace the inheritance of sex-linked characters such as haemophilia?
A pedigree chart
- males represented as a square
- female is a circle
- shading within either shape indicated the presence of a character in the phenotype.
In humans how many pairs of chromosomes carry the genes that determine different characteristics?
23 pairs
What does it means when two genes that occur on the same chromosome?
Said to be linked.
What is an autosome?
Genes carried on the sex chromosome are sex-linked. The remaining 22 chromosomes other than sex chromosomes.
What is autosomal linkage?
The situation where two or more genes are carried on the same autosome.
When does Epistasis arise?
when the allele of one gene affects or masks the expression of another in the phenotype.
Give an example of epistasis
Mice coat colour
- black = melanin
- white = no melanin
- Grey-brown = agouti
- Expression of gene A (black bands) affected by expression of gene B (melanin production)
- If gene B is in the homozygous recessive state (bb) then no melanin is produced and the coat is albino
- Absence of melanin, gene A cannot be expressed.
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