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Course: Middle school biology - NGSS > Unit 7
Lesson 5: Reproduction and genetic variation- Sexual reproduction and genetic variation
- Sexual reproduction and genetic variation
- Genetics vocabulary
- Worked examples: Punnett squares
- Genetics vocabulary and Punnett squares
- Understand: sexual reproduction and genetic variation
- Apply: genetics vocabulary
- Apply: Punnett squares
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Sexual reproduction and genetic variation
In sexually reproducing organisms, each parent contributes half of the genes acquired (at random) by the offspring. Individuals have two of each chromosome and hence two alleles of each gene, one acquired from each parent. These versions may be identical or may differ from each other. Created by Khan Academy.
Want to join the conversation?
- There are no same people, right? Everybody is unique, right?(7 votes)
- yes. nobody is the same allthough there can be simularity(20 votes)
- What if a Therizinosaurus married a Utahraptor? Perhaps a raptor with long finger claws and massive toe claws!(4 votes)
- Usually, two different species can't reproduce successfully. That might be a bit like trying to breed a dog and a cat to produce a dog-cat: it doesn't work out.(10 votes)
- Is it possible for grandparents to have genetic traits that neither of the parents have but the kids do? e.g.: grandma+ grandpa have green eyes, mom and dad have brown eyes, kids have green eyes(2 votes)
- Yes it is possible. Sometimes genes skip a generation(12 votes)
- what is a molosigotige twin?(6 votes)
- Monozygotic twins, (which you may be talking about) are identical twins of the same gender.(3 votes)
- Does this mean that parents can have up to 46 biological kids?(4 votes)
- the most children ever a woman had is 44. but Genghis Khan had up to 3,000 children(1 vote)
- if offspring get two chromosomes from each of its parents, how can it have homologous pairs? shouldn't chromosomes in pairs be the same in shape and gene?(3 votes)
- While it's true that homologous pairs of chromosomes should have the same genes, they can differ slightly in shape and size. This is because each parent may have slightly different versions of the same gene, which can result in variations in the physical appearance of the chromosome. However, the genes themselves will still be present in the same locations on both chromosomes of the homologous pair.(3 votes)
- How do you pronounce "alleles"? Is it "aleels", "alelles", or neither?(2 votes)
- According to Merriam-Webster Dictionary, it’s pronounced like uhleelz.(4 votes)
- is it possible for a human to have a kid by her self and not with a boy?(2 votes)
- yes my mom did it(3 votes)
- if offspring get two chromosomes from each of its parents, how can it have homologous pairs? shouldn't chromosomes in pairs be the same in shape and gene?(3 votes)
- is it possible to have a trisomy on the sex chromosomes? if so, do you have both male and female reproductive parts or does the sry gene take care of the problem?(3 votes)
Video transcript
- [Narrator] Have you ever wondered why children often look a little similar but also very different from
their biological parents, or even how biological siblings tend to share some common features but still have different
traits from each other? To answer this question, we have to go beyond the physical traits that we see in these family portraits and dive into genetic inheritance. In this video, we're going to see that
it's sexual reproduction, a mechanism used by many
organisms to produce offspring, that creates the diversity of traits that exist in biological families and in animal and plant
populations all around the world. Let's start from the beginning. All life comes from other life through the process of reproduction. Parents reproduce to form offspring, and during this process, they pass on their genetic
information to their offspring. During sexual reproduction,
two parents produce offspring. So each offspring gets a
mixture of genetic information from two parents. Parents pass this genetic
information to their offspring via chromosomes, the
coiled up DNA molecules found inside your cells
that contain genes. Sexually reproducing organisms often have many different chromosomes, each containing specific genes. For example, this diagram represents a complete set of human chromosomes. As we can see, there are
23 different chromosomes assigned numbers one through 23. However, there are two
copies of each chromosome, so that there are 23 chromosome pairs instead of 23 single chromosomes. Each chromosome pair is a homologous pair, which means that the two
chromosomes are the same size and contain the same
genes in the same order. However, the alleles on the
two homologous chromosomes may be different, meaning that the chromosomes may not exactly have the
same genetic information. Also, in case you're wondering, the last chromosome set
is a little different, because that chromosome 23
is the human sex chromosome, which influences the biological
sex of the individual, but we don't have to
get into that just yet. What's important to know for our purposes is that sexually reproducing organisms with two sets of chromosomes
in each of their cells are called diploid. Diploid organisms, the
D-I, di indicating two, have cells with two sets of chromosomes that are organized into homologous pairs. Sexual reproduction occurs through a process called fertilization, and during fertilization, cells called gametes, which
are egg and sperm cells, fuse to form a new organism. Each parent contributes one gamete. So you might be wondering, if each of the parents'
organism cells are diploid, and offspring result from the fusion of cells from two parents, how do the offspring
of sexual reproduction maintain the same number of chromosomes? Well, diploid organisms
form gait that are haploid, meaning that they only contain
one set of chromosomes. When you hear the word
haploid, you can think of half, because haploid cells have half the amount of genetic information
than diploid cells have. A human haploid gamete, for example, contains 23 single chromosomes,
one of each homologous pair. When gametes fuse during fertilization, that brings the total number
of chromosomes back to 46, or 23 homologous pairs. So why is sexual
reproduction so important? Well, not only does it allow
organisms to produce offspring, but it also creates genetic
variation and diversity. The reason that offspring
have different traits compared to their parents, and that one sibling looks
different from another, can be attributed to sexual reproduction. This diagram here helps
illustrate how sexual reproduction creates genetic variation. The diagram shows a cross
between two hypothetical parents. It shows the chromosomes and the possible gametes
that the parents can form, and the possible chromosome
combinations in the offspring. So in the diagram, we can see that each
possible parent gamete contains one chromosome
from a homologous pair, and during fertilization, gametes from each parent fuse together, resulting in offspring that have a combination of
chromosomes from both parents, and this is where the genetic variability between parents and offspring comes from. Offspring are not genetically
identical to either parent because they contain a
mixture of genes from both. The diagram also shows us that, because each parent passes
on only one chromosome from each homologous pair, there are multiple
combinations of chromosomes that can occur in the offspring. For example, the pink
chromosome from parent one can be paired with the dark
chromosome from parent two in one offspring, and the light blue
chromosome from parent two in another offspring. Keep in mind that this diagram
only shows the inheritance of a single chromosome, but in humans, this occurs
for all 23 of our chromosomes, and as a result, there are millions of different
chromosome combinations that an offspring can inherit. This is why siblings can look
alike, but aren't identical. Even more mind blowing, there are other genetic processes that occur during fertilization that increase variation even more, resulting in trillions of
possible allele combinations for each offspring. This is why no two people
except monozygotic twins are genetically alike. To summarize, we learned that
sexual reproduction occurs when two haploid gametes fuse
together in fertilization, creating a diploid offspring with homologous chromosome pairs. We also learned that the patterns
of chromosome inheritance during sexual reproduction lead to genetic variation
in families and populations. It's why children look different from their biological
parents, brothers, or sisters. We've all inherited
different sets of chromosomes because of sexual reproduction, which in turn makes each and
every one of us one of a kind.