Biology Punnet Square Summative

Distinguish between chromosomes, sister chromatids, and homologous pairs.

A chromosome is a single, thread-like structure made of DNA that carries genetic information, while sister chromatids are identical copies of a chromosome created during DNA replication, joined together at the centromere; a homologous pair refers to two chromosomes, one from each parent, that carry the same genes but may have different alleles, forming a matching set within a cell.

Define gene and allele.

A gene is a piece of DNA that tells your body how to make something, like a protein. An allele is a different version of a gene. For example, a gene for eye color might have alleles for blue or brown eyes.

Outline the difference between diploid and haploid cells.

A diploid cell contains two complete sets of chromosomes, while a haploid cell contains only one set of chromosomes

Outline the difference between autosomal chromosomes and sex chromosomes.

Autosomal chromosomes are any chromosome in a cell that is not a sex chromosome, meaning they do not determine an individual's sex, while sex chromosomes (like the X and Y in humans) are the specific pair of chromosomes responsible for determining an individual's sex; in humans, autosomes are the first 22 pairs of chromosomes, while the 23rd pair is the sex chromosomes.

Meiosis

2 consecutive cell divisions to produce 4 haploid gametes.

Be able to identify the hallmarks of each stage of Meiosis 1 and Meiosis 2.

Meiosis I:

Prophase I- Homologous chromosomes pair up (synapsis) to form tetrads; Crossing over occurs, allowing genetic recombination; Chromosomes condense and become visible.

Metaphase I- Tetrads line up at the metaphase plate; Spindle fibers attach to kinetochores of homologous chromosomes.

Anaphase I- Homologous chromosomes are pulled apart to opposite poles; Sister chromatids remain attached at this stage.

Telophase I- Chromosomes may de-condense and nuclear envelopes may reform; The cell divides through cytokinesis, resulting in two haploid cells.

Meiosis II:

Prophase II- Chromosomes condense again if they de-condensed in Telophase I; Spindle fibers form and attach to the kinetochores of sister chromatids.

Metaphase II- Chromosomes line up individually along the metaphase plate.

Anaphase II- Sister chromatids are pulled apart to opposite poles.

Telophase II- Chromatids reach the poles and begin to decondense; Nuclear envelopes reform around each set of chromosomes; The cell divides through cytokinesis, resulting in four haploid gametes.

Explain how crossing over, independent assortment, and sexual reproduction each increase genetic variation within a population.

Crossing over happens when chromosomes exchange pieces of DNA during meiosis, creating new allele combinations. Independent assortment ensures that chromosomes are randomly arranged and separated into gametes, leading to different gene combinations. Sexual reproduction combines genes from two parents, producing offspring with unique traits.

Outline the differences and similarities between spermatogenesis and oogenesis.

Spermatogenesis happens in the testes and makes four sperm that are small and able to move. Oogenesis takes place in the ovaries and usually produces one big egg and three smaller, non-viable polar bodies. Spermatogenesis starts at puberty and keeps going, while oogenesis begins before birth, pauses, and follows a monthly cycle after puberty.

Define nondisjunction and describe whether it is more problematic if it occurs in Meiosis 1 or Meiosis 2 and why?

Nondisjunction is when chromosomes don't separate properly during cell division, leading to gametes with too many or too few chromosomes. It's more problematic if it happens in Meiosis I because it affects both pairs of homologous chromosomes, resulting in two gametes with an extra chromosome and two with one less. This increases the chance of serious issues in the offspring. In Meiosis II, only the sister chromatids are affected, which results in two normal gametes and two abnormal ones.

Outline the differences between trisomy and monosomy.

Trisomy and monosomy are two conditions related to chromosome numbers. Trisomy occurs when there are three copies of a chromosome instead of two, like in Down syndrome, which is caused by an extra chromosome 21. Monosomy, on the other hand, happens when there's only one copy of a chromosome, such as in Turner syndrome, where females have just one X chromosome. Both conditions can lead to various health and developmental issues, but trisomy involves having extra genetic material, while monosomy means missing some.

Describe one syndrome that results from a trisomy or monosomy, including symptoms and whether a sex chromosome or autosomal chromosome is affected.

One example of a syndrome that results from trisomy is Down syndrome, which occurs when there is an extra copy of chromosome 21. Symptoms include developmental delays, distinct facial features (like a flat facial profile and slanted eyes), and an increased risk of certain health issues, such as heart defects and hearing problems. Down syndrome affects an autosomal chromosome, specifically chromosome 21.

Discuss the impacts to the chromosome of translocation, inversion, and duplication events.

Translocation, inversion, and duplication are changes that can happen to chromosomes and affect genetic information. Translocation occurs when a piece of one chromosome breaks off and attaches to another chromosome, which can disrupt genes and lead to conditions like certain cancers. Inversion happens when a chromosome segment flips around and reattaches, potentially messing up gene function and causing problems during reproduction. Duplication involves copying a segment of a chromosome, resulting in extra genes, which can lead to developmental issues or diseases.

State the difference between self-pollination and cross-pollination?

Self-pollination happens when a flower uses its own pollen to fertilize its ovules, creating seeds that are similar to the parent plant. Cross-pollination is when pollen from one flower fertilizes the ovules of another flower, leading to more diverse offspring. So, self-pollination results in uniform traits, while cross-pollination can create a mix of different traits.

Describe Mendel's experiments (pick a trait such as purple x white flowers). Include the parental, F1, and F2 generations.

Mendel's experiments with pea plants focused on flower color, specifically crossing purple and white flowers. He started with purebred plants, one with purple flowers and one with white. When he crossed them, all the offspring (F1 generation) had purple flowers, showing that purple is the dominant trait. Then, when the F1 plants self-pollinated, the next generation (F2) had a mix of purple and white flowers in a ratio of about 3:1. This meant that the white trait wasn't gone; it was just hidden in the F1 generation.

State the ratio of dominant to recessive traits that Mendel discovered in the F2 generation.

Mendel discovered a ratio of about 3:1 for dominant to recessive traits in the F2 generation. This means that for every three plants showing the dominant trait, there was one plant showing the recessive trait.

State the Law of Segregation and the Law of Independent Assortment. Explain how these are related to Meiosis.

The Law of Segregation says that during gamete formation, the two alleles for a trait separate, so each gamete gets only one allele. The Law of Independent Assortment states that alleles for different traits are distributed randomly to gametes. The Law of Segregation is observed during Anaphase I of meiosis when homologous chromosomes are pulled apart, ensuring that each gamete receives only one allele from each pair. The Law of Independent Assortment is mainly seen during Metaphase I, when different pairs of homologous chromosomes align randomly at the metaphase plate, leading to the independent distribution of alleles for different traits.

What ratio did Mendel discover in the F2 generation of a dihybrid cross?

Mendel discovered a ratio of 9:3:3:1 in the F2 generation of a dihybrid cross. This ratio represents the phenotypes of the offspring when two traits are considered together: 9 showing both dominant traits, 3 showing one dominant and one recessive trait, another 3 showing the other dominant and recessive trait, and 1 showing both recessive traits.

Describe how and why a testcross is conducted.

A testcross is used to figure out whether an individual with a dominant trait is homozygous dominant or heterozygous. To do this, you cross the individual with a homozygous recessive partner, which has two recessive alleles. If all the offspring show the dominant trait, the tested individual is likely homozygous dominant. If some offspring show the recessive trait, then the tested individual is heterozygous. This simple method helps determine the genetic makeup of the individual with the dominant trait.

Briefly outline the difference between Incomplete Dominance, Codominance, and Polygenic Inheritance.

Incomplete Dominance is when the offspring's traits blend together, like mixing red and white flowers to get pink ones.

Codominance is when both traits are fully shown at the same time, like having AB blood type, where both A and B traits are visible.

Polygenic Inheritance involves multiple genes affecting one trait, resulting in a wide range of possibilities, like skin color or height in people, rather than just a few distinct options.

Explain why genes near each other on the same chromosome tend to be inherited together? The inheritance of such genes does not follow which of Mendel's laws?

Genes that are close together on the same chromosome tend to be inherited together because they are less likely to be separated during crossing over in meiosis. This means they usually get passed on as a group. This pattern doesn't follow Mendel's Law of Independent Assortment, which says that different traits should be inherited independently of each other. Since linked genes are inherited together, they don't assort independently, leading to unexpected combinations of traits.

Describe how a person can be a carrier for a disease.

A person can be a carrier for a genetic disease if they have one normal allele and one mutated allele for a recessive gene. This means they do not show symptoms of the disease because the normal allele is enough to prevent it. However, they can pass the mutated allele to their children. If a child inherits the mutated allele from both parents, they could develop the disease. For example, a person who carries the allele for cystic fibrosis has one normal CFTR gene and one mutated gene but does not have the disease themselves.

If a heterozygous carrier marries another heterozygous carrier, determine the chances that a child will inherit a homozygous recessive disorder?

If two heterozygous carriers (both with the genotype "Aa") have a child, there's a 25% chance that the child will inherit a homozygous recessive disorder (genotype "aa").

If a heterozygous carrier has a gene for a dominant disorder, determine the chances their child will inherit the disorder even if they marry a homozygous recessive person?

If a heterozygous carrier of a dominant disorder (genotype "Dd") has a child with a homozygous recessive person (genotype "dd"), there is a 50% chance that their child will inherit the disorder.

Explain why sex-linked traits such as colorblindness and hemophilia are more common in males than females.

Sex-linked traits like color blindness and hemophilia are more common in males because these traits are found on the X chromosome. Males have one X and one Y chromosome (XY), so if they inherit a recessive allele on the X chromosome, they will show the trait since there's no second X to mask it. Females have two X chromosomes (XX), so they need to inherit the recessive allele from both parents to express the trait. This makes it less likely for females to have these conditions, which is why they are more common in males.

Summarize what a pedigree is.

A pedigree is a family tree that shows how traits and genetic conditions are passed down through generations. It uses shapes to represent people—squares for males and circles for females—and lines to connect parents to their children. Pedigrees help track which family members have certain traits or genetic disorders, making it easier to see how these traits are inherited.

Explain the relationship between genes and alleles.

Genes are pieces of DNA that determine traits in living things, like flower color. Alleles are different versions of a gene. For instance, a gene for flower color could have one allele for purple flowers and another for white flowers. Each person gets two alleles for each gene—one from each parent—and these combinations help shape their traits. So, genes are the basic instructions, and alleles are the variations that add diversity.

Distinguish between genotype and phenotype.

Genotype refers to the specific genetic makeup of an individual, including the alleles they have for a particular gene (e.g., "AA," "Aa," or "aa"). In contrast, phenotype is the observable physical or biochemical characteristics that result from the genotype, such as flower color, height, or eye color. So, genotype is about the genetic code, while phenotype is about how those genes are expressed in appearance or traits.

Explain the multiple allele pattern of ABO blood type- which are dominant, which are recessive.

The ABO blood type system has three alleles: A, B, and O. A and B are codominant, which means if both are present, they both show up, resulting in type AB blood. The O allele is recessive, so it only shows up as type O blood when there are no A or B alleles. Here's how it works: AA or AO gives you type A blood, BB or BO gives you type B blood, AB gives you type AB blood, and OO gives you type O blood. So, A and B are dominant over O, and when A and B are together, they are both expressed.

Describe the modes of inheritance that do not follow Mendel's rules (one gene, two alleles - dominant or recessive). Be able to give an example of each.

Incomplete dominance occurs when neither allele is completely dominant, resulting in a blended phenotype, like when a red flower crossed with a white flower produces pink flowers. Codominance is when both alleles are fully expressed, as seen in AB blood type, where both A and B alleles appear. Multiple alleles involve more than two alleles for a gene, like the ABO blood type system with A, B, and O alleles. Polygenic inheritance happens when multiple genes influence a single trait, such as human skin color, leading to many shades. Lastly, epistasis occurs when one gene affects the expression of another, like in certain dog breeds where a gene can mask the color produced by another gene.

State a type of dominant, recessive, and x-linked disease that follows Mendel's laws of inheritance.

A type of dominant disease that follows Mendel's laws of inheritance is Huntington's disease, which is caused by a mutation in a single gene and can be passed down if one parent carries the dominant allele. A recessive disease is cystic fibrosis, which requires both parents to pass on the recessive allele for a child to be affected. An example of an X-linked disease is hemophilia, where the mutated gene is located on the X chromosome, making it more common in males who have only one X chromosome.