Zygosity in Genetics

Zygosity in genetics is the degree of similarity between alleles at a gene locus, influencing traits and inheritance. It includes homozygosity, heterozygosity, hemizygosity, nullizygosity, autozygosity, and allozygosity. These concepts are pivotal in understanding genetic diversity, diseases, and twin studies, offering insights into genetic inheritance and the role of environmental factors.

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Exploring the Concept of Zygosity in Genetics

Zygosity is a key term in genetics that refers to the similarity or difference of alleles for a specific gene in an organism. Alleles are alternative forms of a gene that occur due to variations in the DNA sequence. In organisms with two sets of chromosomes, known as diploids, each gene is found on both chromosomes of a pair. An organism is homozygous if it has two identical alleles at a gene locus, heterozygous if the alleles are different, hemizygous if only one allele is present, and nullizygous if both alleles are missing. The specific combination of alleles, or genotype, at a locus determines the phenotype—the observable characteristics of an organism.
Identical twins with brown hair and plain t-shirts flanked by fraternal twins with different hair and features, in a neutral indoor setting.

The Diversity and Distribution of Alleles in Populations

Alleles exhibit a broad range of variation within populations, contributing to the genetic diversity of species. While some genes may have only a single allele due to low variation or because alternative alleles are deleterious, most genes have multiple alleles. The frequency and distribution of these alleles can vary, with some being common and others rare. Certain alleles may be associated with genetic disorders, while others may be neutral or beneficial. The pattern of allele inheritance from parents to offspring dictates an individual's zygosity and genetic composition, which is crucial for species survival and adaptation.

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1

Meaning of homozygous

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Organism with two identical alleles at a gene locus.

2

Meaning of heterozygous

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Organism with two different alleles at a gene locus.

3

Difference between hemizygous and nullizygous

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Hemizygous: one allele present. Nullizygous: both alleles missing.

4

Most genes possess ______ alleles, enhancing variation.

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multiple

5

The frequency of alleles within a population can be ______ or rare.

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common

6

Certain alleles might be linked to ______ disorders.

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genetic

7

An individual's ______ and genetic makeup are determined by how alleles are inherited.

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zygosity

8

The survival and ______ of species depend on genetic diversity.

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adaptation

9

Definition of Homozygosity

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Condition where two alleles at a gene locus are identical.

10

Significance of Homozygous-Dominant

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Expresses dominant trait, symbolized by two uppercase letters (e.g., 'AA').

11

Role of Homozygosity in Progeny

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Determines trait inheritance and expression in offspring.

12

In genetics, ______ refers to the presence of two distinct alleles at the same gene position.

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Heterozygosity

13

A heterozygous genotype is represented by one ______ (dominant) and one ______ (recessive) letter, like 'Aa'.

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uppercase lowercase

14

Individuals with heterozygous genes usually express the ______ trait but also have the ______ allele.

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dominant recessive

15

The phenomenon where heterozygosity leads to greater ______ fitness compared to homozygous forms is known as ______ advantage.

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biological heterozygote

16

Definition of Hemizygosity

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Presence of a single allele at a gene locus in a diploid organism, due to gene deletion or sex chromosome genes.

17

Hemizygosity in Human Males

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Males have one X and one Y chromosome, making them hemizygous for most X chromosome genes.

18

Hemizygosity vs Autosomal Gene Inheritance

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Sex-linked traits inherited via hemizygosity show different patterns than autosomal genes, often affecting males more.

19

______ refers to the condition where both alleles at a gene locus are nonfunctional, leading to no gene expression.

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Nullizygosity

20

Meaning of autozygosity

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Condition where both alleles at a locus come from a common ancestor and are IBD.

21

Meaning of allozygosity

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Condition where alleles at a locus come from different ancestors and are IBS.

22

Autozygous genotypes vs. allozygous genotypes

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Autozygous genotypes are always homozygous; allozygous genotypes can be homozygous or heterozygous.

23

______ twins come from one zygote that splits, resulting in genetically identical offspring.

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Monozygotic (identical)

24

______ twins are born when two separate eggs are fertilized by two distinct sperm, leading to genetically distinct siblings.

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Dizygotic (fraternal)

25

______ twins are a rare type, formed when two sperm fertilize a single egg which then divides.

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Sesquizygotic

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