17) Inheritance (4.11) Flashcards
1.1. What are chromosomes made of?
DNA, which contains genetic information in the form of genes
1.2. Define a gene
A length of DNA that codes for a protein
1.3. Define an allele
An alternative form of a gene
1.4. Describe the inheritance of sex in humans with reference to X and Y chromosomes
Sex is determined by a chromosome pair (most other characteristics are just determined by one or a number of genes)
AFABs have XX and AMABS have XY
Half (125 million) of the sperm will be carrying the X chromosome, and the other half carries the Y chromosome, so the father is responsible for determining the gender of the offspring
All egg cells carry an X chromosome
1.5. What determines the sequence of amino acids used to make a specific protein
The sequence of bases in a gene
1.6. What gives different shapes to protein molecules?
Different sequences of amino acids give different shapes to protein molecules
1.7. Explain how DNA controls cell function
By controlling the production of proteins, including enzymes, membrane carriers and receptors for neurotransmitters
1.8. Explain how a protein is made
(a) The gene coding for the protein remains in the nucleus
(b) Messenger RNA (mRNA) is a copy of a gene
(c) mRNA molecules are made in the nucleus and move to the cytoplasm
(d) The mRNA passes through ribosomes, which read the code in groups of three
(e) The ribosome assembles amino acids into protein molecules
(f) The specific sequence of amino acids is determined by the sequence of bases in the mRNA
1.9. Why are some genes not expressed?
Most body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs
1.10. Describe a haploid nucleus
A nucleus containing a single set of chromosomes
1.11. Describe a diploid nucleus
A nucleus containing two sets of chromosomes
1.12. How many chromosomes are there in a diploid cell?
A pair of each type of chromosome and in a human diploid cell there are 23 pairs
2.1. Describe mitosis
Nuclear division giving rise to genetically identical cells
2.2. State the role of mitosis
Growth, repair of damaged tissues, replacement of cells and asexual reproduction
2.3. When does the exact replication of chromosomes occur?
Before mitosis
2.4. What happens during mitosis?
The copies of chromosomes separate, maintaining the chromosome number in each daughter cell
2.5. Describe stem cells
Unspecialised cells divide by mitosis to produce daughter cells that can become specialised for specific functions
3.1. What is meiosis involved in?
The production of gametes
3.1. What is meiosis involved in?
The production of gametes
3.2. Describe meiosis
A reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells
4.1. Describe inheritance
The transmission of genetic information from generation to generation
4.2. Describe genotype
The genetic make-up of an organism and in terms of the alleles present
4.3. Describe phenotype
The observable features of an organism
4.4. Describe homozygous
Having two identical alleles of a particular gene
4.5. What is pure-breeding?
Two identical homozygous individuals that breed together
4.6. Describe heterozygous
Having two different alleles of a particular gene
4.7. Can a heterozygous individual be pure-breeding?
No
4.8. Describe a dominant allele
An allele that is expressed if it is present in the genotype
4.9 Describe a recessive allele
An allele that is only expressed when there is no dominant allele of the gene present in the genotype
4.11. Use genetic diagrams to predict the results of monohybrid crosses and calculate phenotypic ratios
Aa x aa = 1:1 ratio
Aa x Aa = 3:1 ratio
4.13. Explain how to use a test cross to identify an unknown genotype
Crossing with a recessive is called a test cross (or back cross), which tells us if an unknown dominant phenotype is heterozygous or homozygous
Homozygous: all the offspring will have the dominant allele
Heterozygous: 1 : 1 ratio of dominant : recessive allele
