Biology Unit 2 SAC - How does inheritance impact on diversity

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Describe the structure and function of nucleic acids, with reference to DNA and RNA

Describe the structure and function of nucleic acids, with reference to DNA and RNA

Nucleic acids are biomolecules that store and transmit genetic information.

DNA is double-stranded and contains deoxyribose sugar, while RNA is single-stranded and contains ribose sugar. Both have nucleotides made of a phosphate group, sugar, and nitrogenous base.

DNA carries genetic instructions for cell functioning and heredity, while RNA helps in protein synthesis and gene expression.

Distinguish between a gene, allele and genome

A gene is a segment of DNA that contains instructions for building a protein or RNA molecule. An allele is a variant form of a gene, leading to different traits. A genome is an organism's complete set of genetic material, including all genes. In short, a gene is a DNA segment, an allele is a gene variant, and a genome is an organism's entire genetic material.

Describe the structure of a chromosome, with reference to key features

A chromosome is a thread-like structure in the nucleus of a cell. It has DNA coiled around proteins called histones. Key features include the centromere, telomeres, chromatids, genes, chromatin, and karyotype. Chromosomes organize, replicate, and transmit genetic information during cell division and inheritance.

Describe the nature of pairs of homologous chromosomes, with reference to carrying the same gene loci

Homologous chromosomes are pairs with same genes at same loci. They're similar in size, shape, and carry genetic info for same traits. Each pair has one chromosome from mother and one from father. They align during meiosis for genetic recombination and material exchange. Homologous chromosomes are key for genetic inheritance and diversity of offspring.

Describe the number of an organisms chromosomes using diploid and haploid

The number of chromosomes in an organism can be diploid (2n) or haploid (n). Humans have a diploid number of 46 (2n=46), with 23 pairs of chromosomes from each parent. The haploid number in humans is 23 (n=23), representing chromosomes in reproductive cells. This distinction is important in genetics and reproduction.

Distinguish between autosomes and sex chromosomes in the context of a karyotype

Autosomes and sex chromosomes are two types of chromosomes in a karyotype. Autosomes are non-sex chromosomes found in both males and females, determining most genetic traits. Humans have 22 pairs of autosomes. Sex chromosomes determine biological sex: females have two X chromosomes (XX), males have one X and one Y chromosome (XY). Sex chromosomes influence reproductive organ development and secondary sexual characteristics.

What are the different chromosomal variations when analysing a karyotype?

Monoploidy - where the cell or organism has a functional genome consisting of one copy of each chromosome

Polyploidy - when the cell or organism has a genome with three or more copies of each chromosome (all)

Aneuploidy - when the cell or organism varies in the usual number of chromosomes in its genome b the addition or loss of a chromosome. (caused by failure of separation of chromatids in anaphase/meiosis)

trisomy = one extra chromosome

monosomy = one less chromosome

Describe the process of transcription with reference to initiation, elongation and termination

Transcription is the essential process of copying genetic information from DNA to RNA for protein synthesis. Its essential for gene expression:

1. Initiation: RNA polymerase binds to the promoter region on DNA, signalling the start of transcription. The DNA strands separate, and RNA synthesis begins.

2. Elongation: RNA polymerase moves along the DNA template, adding RNA nucleotides to the growing molecule.

3. Termination: Transcription ends when RNA polymerase reaches a termination sequence on DNA. (stop codons) The polymerase detaches from the template, releasing the newly synthesized polypeptide chain.

Compare start/stop codons, exons and introns

Start/stop codons, exons, and introns are important components of gene expression in organisms. Start codons signal the beginning of protein synthesis, while stop codons indicate its termination. Exons contain the instructions for protein synthesis, while introns are non-coding regions that are removed during mRNA processing.

Describe mRNA splicing

mRNA splicing is a process in the cell's nucleus where non-coding sections (introns) are cut out from a precursor mRNA and the remaining coding sections (exons) are joined together. This creates a mature mRNA that can leave the nucleus and be used as a template to build proteins. This process increases the diversity of proteins that can be made from a single gene.

Describe the process of translation, with reference to initiation, elongation and termination

Translation is the process of building proteins from mRNA instructions. Initiation starts with a ribosome attaching to mRNA, elongation adds amino acids to the growing protein chain, and termination ends the process at a stop codon, releasing the completed protein.

Compare somatic cells and gametes, with reference to the number of chromosomes how and they’re produced

Somatic cells are regular body cells, while gametes are reproductive cells like egg and sperm. Somatic cells have two sets of chromosomes (diploid), one from each parent, produced through cell division. Gametes have one set (haploid), formed through a special type of cell division called meiosis, which halves the chromosome number to ensure genetic diversity when fertilization occurs.

Describe the process of meiosis and compare the differences in stages

Meiosis is the cell division process that creates reproductive cells (gametes) with half the usual number of chromosomes. It involves two rounds of division (meiosis I and meiosis II) and produces four unique haploid cells, each with a mix of genetic material for genetic diversity. Meiosis I involves the separation of homologous chromosomes, while meiosis II focuses on the separation of chromatids.

Describe the significance of crossing over chromatids and independent assortment for genetic diversity

In combination, crossing over and independent assortment introduce significant genetic variability among offspring, increasing their chances of adapting to changing environments and promoting the survival and evolution of species.

How do you compare and distinguish dominant and recessive alleles?

Dominant alleles express their traits in both heterozygous and homozygous states, while recessive alleles only show their traits in homozygous condition. Dominant alleles mask the effects of recessive alleles when present together.

Compare the modes of inheritance: complete, co and incomplete dominance

Complete Dominance:

- One allele is dominant, masking the expression of the recessive allele.

- Heterozygous phenotype is the same as the homozygous dominant phenotype.

- Example: Yellow (dominant) and green (recessive) pea seeds.

Codominance:

- Both alleles are fully expressed in the heterozygous genotype.

- Phenotype shows characteristics of both alleles.

- Example: AB blood type in humans (both A and B alleles expressed).

Incomplete Dominance:

- Neither allele is dominant; heterozygous phenotype is a blend of both alleles.

- Phenotype appears as an intermediate between the homozygous genotypes.

- Example: Pink flowers from crossing red and white flowers.

Explain how sex-linked genes are inherited

Sex-linked genes are on the X and Y chromosomes. In males (XY), X-linked genes are expressed since they lack a second X. In females (XX), both X-linked alleles can influence traits. Examples: Hemophilia and color blindness are X-linked recessive traits, impacting males more.

Benefit of punnet squares and test cross

Punnet squares assist in visualizing genetic probabilities, aiding in predicting offspring traits, while test crosses reveal the genotype of individuals with dominant phenotypes.

Describe how an organisms phenotype is dependent on interactions between its genes and the environment

An organism's phenotype is influenced by both its genes and the environment. Genes provide the instructions, but environmental factors can affect how those instructions are carried out, leading to variations in observable traits.

e.g) the himalayan rabbits fur turns black when it is cold and lacks protein

Explain how epigenetics can change an organisms phenotype through modifying gene expression

Epigenetics modifies gene expression without altering DNA sequence. Chemical changes to DNA and histones influence gene accessibility, impacting phenotype.

DNA Methylation: Adding a methyl group to DNA can silence genes, affecting phenotype. For instance, DNA methylation can turn off genes associated with embryonic development in adult cells.

Histone Modification: Chemical changes to histones alter DNA packaging. Methylation can either activate or repress genes.