Ch. 16 - Chromosomes, Genes and Proteins
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What is DNA?
DNA refers to a long thread of genetic information, in the form of genes, which control the proteins made by a cell.
What is a chromosome?
A chromosome is a compact form of DNA, coiled. It is a length of DNA that contains genetic information in the form of many different genes. It is found in the nucleus.
What are genes?
Genes are lengths of DNA which code for a specific protein.
What are genotypes?
Genotype refers to the genetic makeup of an organism in terms of the alleles present.
What are phenotypes?
Phenotype refers to observable feature of an organism.
What is an allele?
An allele is an alternative form of a gene.
What is a dominant allele?
A dominant allele is an allele which is expressed.
What is a recessive allele?
A recessive allele is an allele which is only expressed when the dominant allele is not present.
What is a carrier?
A carrier is a gene which is carrying a recessive allele.
What does homozygous means?
Homozygous refers to an organism has two identical alleles of a particular gene.
What does heterozygous mean?
Heterozygous refers to an organism has two different alleles of a particular gene.
How do genes code for proteins?
The sequence of bases in a gene determines the sequence of amino acids used to make a specific protein, where three bases (one codon) codes for one amino acid.
How many pairs of chromosomes do humans have?
Human cells, excluding gametes, have 23 pairs of chromosomes (46 chromosomes). 22 of those are somatic chromosomes while 1 pair is a sex chromosome.
What are haploid and diploid cells?
Haploid cells - Only 23 chromosomes (a single set) - Gametes Diploid cells - 23 pairs of chromosomes (46 chromosomes in total)
What is codominance?
Codominance: When both alleles are expressed in the phenotype.
Describe the dominance of alleles which decide blood group.
I denotes the gene responsible for blood group: IA and IB are codominant, however both are dominant over IO. Positive and negative is owing to the Rhesus factor.
What is required in a genetic diagram?
• Parental Phenotype • Parental Genotype • Parental Gametes which MUST be circled • Punnett Square • Phenotypic and Genotypic ratio (If asked for in the question)
What are the parts of a pedigree diagram?
• Circle - female • Square - male • line of mating • Line of inheritance
What are sex chromosomes?
Sex chromosomes are chromosomes that determine sex. There are two types: X chromosomes and Y chromosomes. (Genes in sex chromosomes are indicated with an X and a subscript)
What are X and Y chromosomes? Which of these do women and men have?
X chromosomes are the larger of the two sex chromosomes in mammals. Y chromosomes are the smaller of the two sex chromosomes in mammals. Women: XX Men: XY
What are sex linked genes?
Sex linked genes are genes present only in sex chromosomes.
What are sex linked characteristics?
Sex-linked characteristics are features which are caused by genes only located on a sex chromosome. This makes the characteristic more common in one sex than in the other
Describe red-green colour blindness as an example of sex linkage.
As the Y sex chromosome is smaller than the X sex chromosome, certain genes present on X are not present on Y. One example are cone cell genes - indicated by the Gene B. Cone cells are responsible for your ability to see red and green. XBXB - normal vision female XBXb - normal vision but carrier female XbXb - colourblind female XBY - normal vision male XbY - colourblind male
What are homologous chromosomes?
Homologous chromosomes are chromosomes which: 1. Do not have identical sequences 2. Have the same gene for a particular characteristic, at the same location 3. One half of the set is comes from the paternal side, the other from the maternal