Year 10 Science: Genetics, DNA Structure, Cell Division, and Inheritance

Comprehensive practice flashcards covering Year 10 Science topics on DNA structure, DNA replication, mitosis, meiosis, Mendelian inheritance, sex determination, sex linkage, karyotypes, genetic code, and mutations.

Where is DNA located within the cells of living organisms, and what is its primary function?

DNA is located in the nucleus of cells and acts as a biological 'blueprint' containing instructions that govern cell structure, type, and metabolic chemical reactions.

In the laboratory practical on DNA isolation, which organism's fruit was used to physically extract and observe DNA?

Strawberries were used to break down cell structures and isolate DNA from cell nuclei.

What three distinct components make up a single DNA nucleotide?

A deoxyribose sugar molecule ($5$-carbon sugar), a phosphate group ($\text{PO}_4$), and a nitrogenous base (adenine, thymine, cytosine, or guanine).

What is Chargaff's rule regarding the nitrogenous bases in DNA?

The amount of adenine always equals the amount of thymine ($\text{A} = \text{T}$), and the amount of guanine always equals the amount of cytosine ($\text{G} = \text{C}$).

Which historic experimental image is shown here, and what discovery did it enable?

Rosalind Franklin's X-ray crystallography photograph (Photo 51), which James Watson and Francis Crick used to deduce the double-helix structure of DNA.

How many hydrogen bonds form between complementary base pairs in DNA?

Two hydrogen bonds form between adenine ($\text{A}$) and thymine ($\text{T}$), while three hydrogen bonds form between guanine ($\text{G}$) and cytosine ($\text{C}$).

Which DNA nitrogenous bases are classified as purines and which as pyrimidines?

Adenine ($\text{A}$) and guanine ($\text{G}$) are purines; cytosine ($\text{C}$) and thymine ($\text{T}$) are pyrimidines.

What historical forensic mystery was reported to be solved using modern DNA testing mentioned in the lecture?

The identity of Jack the Ripper, who was matched by DNA testing to a Polish immigrant named Aaron Kosminski.

What are the four sequential steps of DNA replication?

1. The DNA double helix unwinds. 2. The enzyme DNA helicase unzips the DNA into separate strands by breaking hydrogen bonds. 3. DNA polymerase adds complementary nucleotides from the cell. 4. Two identical DNA molecules are formed.

Why is DNA replication described as 'semi-conservative'?

Because each newly formed double-stranded DNA molecule retains one original 'parent' strand and synthesises one new complementary strand.

How many total chromosomes are present in a typical human somatic cell before DNA replication, and how many immediately after replication before division?

There are $46$ chromosomes ($23$ pairs) before replication and $92$ chromosomes immediately following replication.

What are the three biological reasons for DNA replication and cell division?

Replacement of damaged cells, growth of the organism, and asexual reproduction (such as binary fission in bacteria).

What is the structural difference between a single unduplicated chromosome and a duplicated chromosome?

An unduplicated chromosome contains a single chromatid, whereas a duplicated chromosome consists of two identical sister chromatids joined together at the centromere.

What are the key differences between mitosis and meiosis in terms of daughter cell number, genetic identity, and ploidy?

Mitosis produces two genetically identical diploid ($2n$) cells for growth and tissue repair; meiosis produces four genetically unique haploid ($n$) gametes for sexual reproduction.

What occurs during the two successive division stages of meiosis (Meiosis I and Meiosis II)?

During Meiosis I, homologous chromosomes separate; during Meiosis II, sister chromatids separate.

What are homologous chromosomes?

Corresponding chromosome pairs that are of the same length, have centromeres in the same position, and carry the same genes in the same loci, with one inherited maternally and one paternally.

What is an allele?

An allele is an alternative form or version of the same gene, situated at the same gene locus on homologous chromosomes.

What were the seven phenotypic traits of pea plants investigated by Gregor Mendel?

Flower colour (purple/white), seed shape (round/wrinkled), seed colour (yellow/green), pod colour (green/yellow), pod shape (inflated/constricted), plant height (tall/short), and flower position (axial/terminal).

In Mendel's monohybrid cross between pure-breeding round ($\text{RR}$) and wrinkled ($\text{rr}$) peas, what were the phenotypes of the $F_1$ and $F_2$ generations?

The $F_1$ generation was $100\%$ round seeds ($\text{Rr}$); self-crossing $F_1$ plants produced an $F_2$ generation with a phenotypic ratio of $3/4$ ($75\%$) round to $1/4$ ($25\%$) wrinkled seeds.

What is the difference between a homozygous and a heterozygous genotype?

A homozygous genotype possesses identical alleles for a trait ($\text{RR}$ or $\text{rr}$), while a heterozygous genotype possesses two different alleles ($\text{Rr}$).

In a monohybrid cross between two heterozygous black-furred rabbits ($\text{Bb} \times \text{Bb}$), what are the expected genotypic and phenotypic ratios?

Genotypic ratio: $1\,\text{BB} : 2\,\text{Bb} : 1\,\text{bb}$; Phenotypic ratio: $3\text{ black fur} : 1\text{ brown fur}$.

How is biological sex determined genetically in human fertilisation?

Females have an $\text{XX}$ genotype and produce eggs carrying an $\text{X}$ chromosome; males have an $\text{XY}$ genotype and produce sperm carrying either an $\text{X}$ or a $\text{Y}$ chromosome. The sperm's chromosome determines the offspring's sex.

What visual assessment test is depicted in this image, and which sex-linked trait does it screen for?

An Ishihara test plate used to identify red-green colour blindness.

Why do males suffer from recessive sex-linked disorders more frequently than females?

Males have only one $\text{X}$ chromosome ($\text{XY}$), meaning a single recessive allele on the $\text{X}$ chromosome causes the disorder; females have two $\text{X}$ chromosomes ($\text{XX}$) and require two copies of the recessive allele to manifest the condition.

Which royal family pedigree is shown below, and which sex-linked genetic disorder does it trace?

Queen Victoria's family tree, illustrating the inheritance of the recessive sex-linked bleeding disorder haemophilia.

What is the biological relationship between genotype, environment, and phenotype?

$\text{Phenotype} = \text{Genotype} + \text{Environment}$; an organism's observable traits (phenotype) result from the expression of its genetic makeup (genotype) modified by environmental factors.

Which human traits listed in the lecture are determined strictly by genotype with no environmental modification?

Blood type and tongue-rolling ability.

What is the fundamental difference between transcription and translation during protein synthesis?

Transcription occurs in the nucleus where a DNA template forms messenger RNA (mRNA); translation occurs in the cytoplasm where mRNA is read by ribosomes to assemble amino acids into a protein.

What are three structural and chemical differences between DNA and RNA?

1. DNA is double-stranded, whereas RNA is single-stranded. 2. DNA contains deoxyribose sugar, whereas RNA contains ribose sugar. 3. DNA uses thymine ($\text{T}$), which is replaced by uracil ($\text{U}$) in RNA.

What is a codon, and what are the specific functions of the start codon and stop codons?

A codon is a triplet sequence of $3$ bases on mRNA. The start codon $\text{AUG}$ initiates translation and codes for methionine; stop codons ($\text{UAA}$, $\text{UAG}$, $\text{UGA}$) terminate translation because they do not code for an amino acid.

Approximately how many genes do humans possess, and what percentage of DNA is shared with fruit flies and chimpanzees respectively?

Humans have approximately $20{,}000$ genes, sharing about $50\%$ of their DNA with fruit flies and $96\%$ with chimpanzees.

Which chromosomal abnormality is represented in this karyotype?

Down Syndrome (Trisomy 21), evidenced by three copies of chromosome $21$, resulting in a total of $47$ chromosomes.

Which genetic condition is characterized by this karyotype showing 45 chromosomes?

Turner's Syndrome, characterized by a missing sex chromosome ($45,\text{X}$).

What is Klinefelter's syndrome, and what karyotype designation defines it?

A condition in males caused by having an extra $\text{X}$ chromosome, resulting in $47$ chromosomes with an $\text{XXY}$ sex chromosome arrangement.

How many total chromosomes are present in diploid cells of dogs and gorillas respectively?

Dogs have $78$ chromosomes ($39$ pairs); gorillas have $48$ chromosomes ($24$ pairs).

What is the difference between a point substitution mutation and a frameshift mutation?

A point substitution replaces a single nucleotide base with another, potentially changing one amino acid; a frameshift mutation inserts or deletes nucleotides, shifting the entire downstream triplet reading frame.

What genetic condition causes the red blood cell shape shown in this micrograph?

Sickle Cell Disease, caused by a single base substitution that alters the amino acid sequence of haemoglobin, producing stiff, crescent-shaped red blood cells.

What percentage of human DNA is non-coding, and what role can mutations in this DNA play?

Approximately $99\%$ of human DNA is non-coding; it functions in gene regulation by turning genes on and off, and mutations here can alter gene expression and phenotype.

What are mutagens, and what three environmental categories of mutagens are identified in the notes?

Mutagens are environmental agents that increase the frequency of DNA mutations; categories include chemicals (e.g., in tobacco), radiation (radioactivity and X-rays), and ultraviolet (UV) light.

What four steps explain how mutations drive natural selection and evolution in a population?

1. Genetic variation arises from mutations. 2. Differential survival occurs due to selective pressures or predators. 3. Genetic inheritance enables surviving parents to pass favorable alleles to offspring. 4. Change over time leads to an increased frequency of the favorable trait in the population.